The majority of people that post on Urban Dictionary are uneducated kids trying their lame excuse at humor. Some of it can be entertaining and right on the money, but much of it is deliberatly offensive, and crudely ignorant.
Here is my favorite definition from the site,
1. bible
An ancient novel full of murder, corruption, homosexuality, bestiality, incest and cruelty. It is often read to children on Sunday.
Now that is good!