Puns
Avoid at all costs, unless told as a spur-of-the-moment joke. Telling people a long joke that ends in a pun will usually result in a slap, a fist to the jaw or a cold, mean look that says "Die. Puns are the devil." However, if you pull off a quick thinking pun, telling it as you think of it, people usually laugh. Puns have got to be short and sweet, like... like... I dunno. Like something.
For instance, the other day at school I was studying a town called Collie, when a pun jumped into my head. Instead of taking a long time to lead up to the pun, telling a long joke and then getting slapped, I just blurted it out. "A flower that grows in Collie is a Collieflower." Cauliflower! Get it! Well, my friends did, and they laughed (and groaned afterwards.) But the important thing is they laughed, because I didn't take my time to tell it. You've got to show your wit; then people can really laugh at you. I mean with you. Laugh with you. Moving on...
No, wait, not moving on. Puns are ultimately the devil, so don't spread them. They're really, really, really naughty.