Oh my! I bet the computer would stop working way before you could do even half of these things. :-D
Lukas

Visit and download from as many p.o.r.n sites as possible, and feel free to follow any links advertised.

Do not protect your computer with a password.  Seriously; why should you have to remember one more thing in life?

Allow everyone in your neighborhood to use your computer at any given moment in time.

if you are on twitter and you see irregular direct messages from your followers containing interesting links, don't hesitate to click on them.  Chances are your twitter will get hacked, and we have no way of knowing what else may follow.

when browsing the net, make sure to disable fishing filters and popup blockers.  Ya wanna make sure to have as many opportunities as possible to test your advanced skils.

Search for fre software and download and install software that will install other software and toolbars, screensavers and other bloatware on your machine.

Trust all instant messages from weird screennames on AIM.

Do not defrag, delete temporary files, check for failed sectors on your hard drive, or run system restore unless your computer is infected already and showing horrible signs.  Your old registry will simply merge with the infected one creating a massive dump across your system.

Well, In firefox I use the adblock plugin, which boy makes a difference. You don't initially notice it, but when I have to use IE for something I realize just how much flash ads use these days.
As for some more ideas, if someone sends you a text document in a .exe file, we all know you should open it. Let all scripts and activeX run, and enable the preview pain in your e-mail client. 
Before purchasing your software, first go ahead and find as many cracks for it as possible, visiting each site youf ind and downloading it, then running said file, and after you're done with that, go and purchase. By this time you  most likely would have gotten a keylogger...
If a site asks for your credit card details, go and supply, since if an email says urgent, it's urgent and must be done ASAP!

When you have a wireless network at home, don't put a password on it! Isn't sharing bandwidth with your neighbours caring? When you have multiple PCs connected to this network, share the contents of all the drives and don't put passwords on them. Afterall, why would hackers want to hack me? Don't they just hack government agencies? Its so troublesome to get file sharing to work when you password-protect it. When browsing your system drive, make sure to delete files with weird extensions on them such as .dll, .dat etc; they're just there to clutter up your hard drive.

oh

o.k here it is,  if you want a hardware failure!
1: just slide the cover of your case open "if you have PC"
(skip this step if you have a labtop)
2: flex your arm muscles and curl your fist.
3: smash your fist powerfully in your case, and try to hit all the hardwares and the cables.
if it didn't do the trick, again smash your fist in it untill you hear a loud "zap!" sound and your pc never gets back online.
(if you have a labtop just throw it at aboute 15 meters to the ground and it'll do the trick)
good luck!

heh ok all above was just kidding but

try searching for torrents and installing all of them. and wait for the malwares to creep to your computer!

Hello

If you really want to mangle your computer for good and i mean for good do the following.

1. Use your computer as a punching bag. Whenever you get mad, sit in your chair and have a temper tantrum kicking at your cpu and pounding your fists on the keyboard. Keep doing this until your cpu starts to crack or dent and your keyboard is missing all the keys and the little button things under the plastic keys get jammed or, while you're still in a rage, pull at the little buttons under the plastic until they pop out in your hands.
Go on the internet and install my security engine. This actually happened to me. I installed something called my security engine that i randomly found when trying to get stuff from l-works. It claims to be an anti-virus program, but it is a virus and has a little chicken thingie that makes squacking noises once in a while and pops up fake warnings of malware on your computer. Hey, you know? When you take a bath or shower, be sure to take your computer with you. After all, you wouldn't want to be interrupted from playing Shades of Doom by a bath would you?
Also, take your computer to school and show it to other kids. They will probably go wild over it and start fighting over it. Someone will eventually break something important.

And, hey please do not do these things.

Wow dark; your friend is insane rofl. Was he so desperate to smoke that he had to use the cd drive as a makeshift ashtray?

@Aprone: yeah that's kinda hard to believe; it had me laughing out loud . The worse that has happened to me is spilling coffee all over the table my laptop was sitting on rofl though thankfully I managed to lift it away in time to avoid most of the coffee.

Hmmm, I didn't think deleting local disk c was even possible! reformat yes, delete no, however I'm not going to try it to find out :d.

Yes victorious, my friend was a litle, mmmm, not in a legal state of mind at the time (as I said, not just tobacco he was smoking), .

Hi,
It's my turn and this one's for the hardware failures, or rather: if someone does do these things and gets frustrated, do the following (this is similar to the rage one)
Note: if anyone does attempt to do anything in this topic it will generally not be good news, the same goes for the following one. I hope that this will help releave stress and cause a laugh though... and some of it probably isn't physically possible anyway, you'll get what I mean when you read it. So, here goes and enjoy!
Grab a hammer in the style of pkb game's pc blaster that was once available (not sure if it is anymore).
Start with the computer keyboard, bringing the hammer dwn. If this does not crush the keyboard in one hit then get an even larger hammer, hire a mechanical arm that can lift it around 50 feet in the air, and let the arm swing down and watch as not only the keyboard is sent showering everywhere but it will probably smash through your desk as well.
If you're really frustrated smash the desk again until it becomes a fine poudery substance.
Next go for the monitor that's probably either already been smashed or is on the floor in a heep. If the latter, grab and rip one side out... slowly... painfully... torture it!
Once that's done, do the same with the other, only this time rip it so fast that the thing just pops off.
Next, the screen part... Try to bend it and attempt to create a monitor metalic aeroplane, and throw it out the window, or if you're really daring and you're in a workplace, find the boss's office and throw it through their window so it lands inside, not out, of it. If you haven't been fired that will certainly get you fired and possibly you may end up paying hundreds or thousands of your local currancy for damages.
Next, go back to your pc and go for the tower. If you're in a workplace it is simply recommended to skip this step and run as the police might be coming after you at this stage. But if you think you can get the tower before they get to where you are then grab it and throw it into your car and prepare for the wildist police chace of your live. If the tower is still turned on and has a speaker inside, jaws for windows might start speaking with pc speaker voices or something. (note, this probably isn't true, but if it was it'd be funny)
Get out your iPhone and load up aradni GPS with voiceover on. Plug it into your car's stereo and have it blaring out so loud with the window open. For an even more daring step, put on sound of da police hiphop song at max volume! The police will still be on your tail and there'll probably not be too much of a way to avoid them.
When you get home, if you still have the mechanical arm, get out of the car with the tower loaded in the arm and launch it at your front door. If like most mechanical arms it's spring loaded, the door and tower will both be smashed. The arm should then swivvel round into any oncoming cars and if you put spikes on the end the result would be very very deadly.
Congratulations, you've successfully become some sort of crazy, nerdy psycopath!
A final note: I hope I haven't offended anyone, really.

hi,
about getting infected
I  forgot about those p0rn sites yeah go and download the flash thingies they give you
and soon you'll have some kind of rootkit
so about running xp with no service packs
1. I plugged in my ethernet cable
2. I forgot to update avira
3. I started ultra-browsing
4. suddenly.... antivir guard: atention: detection! it kept finding files like 72.scr and wierd .exes
it kept detecting the tr/cript.zpack.gen trojan I should have done something but oh no!
I kept browsing
then avira updated and asked me to reboot
I said well k
then the pc booted back up
it detected  a inject trojan
then it detected worm/irc-bot 99999.9 worm
so, I started browsing again
then things started to get nasty
I plugged in my external hdd
then it started detecting w32:virut.gen virus
and soon after it detected the w32:sality.y virus
both viruses are one of the worst viruses you can ever get
then avira was detecting 6 viruses a minute
and I said wow!
time for a scan...
I started a scan
and I made another silly mistake!
I forgot to unplugg my internet cable
and boom
my pc rebooted
and when the desktop came back up...
no avira!
that pc remained infected for another week

is it still disabled?
use  malwarebytes to remove leftover malware traces
you can get it at
www.malwarebytes.org