Here's some representative ATS topics: I tried to pick long-form posts over short-form ones because from what I remember those are supposed to be a little easier to deliver. Most of these are about aliens: there are probably funny topics on other subjects too but the alien ones usually front-load the crazy in the topic title, so they're easy to pick.

http://www.abovetopsecret.com/forum/thread1021341/pg1 - Dolphins were brought here from the Andromeda galaxy to DESTROY THE HUMAN RACE!
http://www.abovetopsecret.com/forum/thread1018027/pg1 - Illuminati love skunks (I am earthling) <- this one is really, really crazy!
http://www.abovetopsecret.com/forum/thread1039525/pg1 - I am a living anime
http://www.abovetopsecret.com/forum/thread980875/pg1 - I've defeated the alien
http://www.abovetopsecret.com/forum/thread978889/pg1 - Bisexual alien wizardry (transitory)
http://www.abovetopsecret.com/forum/thread1037999/pg1 - The real truth about alien anatomy

Just as a grand finale:

http://www.abovetopsecret.com/forum/thread399735/pg1 - Sexy lizardman dating

It's a running story: after the first post, don't miss out on these
- http://www.abovetopsecret.com/forum/thread399735/pg8#pid8843562
- http://www.abovetopsecret.com/forum/thread399735/pg10#pid12593410
- http://www.abovetopsecret.com/forum/thread399735/pg11#pid15992131
- http://www.abovetopsecret.com/forum/thread399735/pg12#pid16024404