Urbandictionary.com, enough said.
urban dictionary is the best slang dictionary ever, period.
Awsome idea that is slowly being overwhelmed by morons who insist on making up complete bullshit words about sex, their boy/girl friend, and every low IQ insight that pops into their minds. Hopefully the book version will weed out all the bullshit.
Dan: Hey I just took a big fucking dump!!
John: Really. Hmmmm. Hey that could be a word!
John: How about.....you just took a Bif-dump!
Dan: Dude, submit it to a slang dictionary like www.Urbandictionary.com
John: Yeah. Ok. I'll do it.