If you put on a mental filter for all the disgusting stuff, you can get a lot of funny out of UD -- especially the UD word of the day, which is never disgusting. (At least, I haven't found any disgusting ones.)
Now, I admit, I posted something that was a little icky -- the term "poop friend" to mean "a friend you're comfortable enough with to talk about pooping" -- but for the most part it's just fun. The problem is that sites like that are infested with 12-year-olds or people with that sense of humor.
Admittedly, I also have the sense of humor of a 12-year-old sometimes.