It's like a dictionary, only that things are bashed, than described.
Describing a thing on urbandictionary.com:
1. mark it as gay
2. get personal
3. use stereotypes
4. use 10 times the word "pretentious"
5. say that people who are common with this are the biggest shit of mankind, killers of seal babies and the cause of your sexual frustration
6. pretend to be individual and type the same stuff, that every other basher said about the described thing
7. send it to UD