[Oni]

I rickrolled everyone in my school using a combination of a few things. Arp poisoned the network then used an ettercap filter with a few other things....also the year before that was ascii goatsee ;D

That's not original.

I went into the computer lab at my school before classes started and unplugged all the computers' power plugs slightly so it looked like they were plugged in and working but none of them worked. Not actually sure if anyone realized what was wrong with the computers or if the tech guy figured it out.

More original and possibly annoying for staff.

Is everyone who posts in this thread going to be banned?

For April Fools? If we hadn't just discussed this idea, I would have.

Just find some one, look them in the eye, laugh and say "soon" and every time you see them keep laughing untill they realise you're not going to do anything, but hopfully they will be paranoid.

And you can get other people involved, see if you can make some one really paranoid about something that just wont happen.

Worked for me, many times

This is evil. I have some paranoid friends that also happen to be quite gullible.