The point is that the urban dictionary is full of bullshit joke/shock-value definitions that are basically not used. To call it as a whole 'true' is rather misleading.
I'm skeptical. My expectation is that the majority of definitions on Urban Dictionary are in fact attested uses of slang-- mainly on the basis that however many people are out there spending their time coming up with "bullshit" slang, there are billions of people making real slang every day. Whatever kind of crazy made-up definition you come up with, someone will come along tomorrow and use an even sillier-sounding word to mean something even weirder.
Keep in mind that that a piece of slang is attested does not necessarily make what it describes real. To choose a rather mundane example, "dick in a box" is defined as a gift-wrapped box with a hole cut in one side, into which a man's penis is inserted, which is then presented as a gift. I'm sure since the term was coined a few people have tried it out, but in general it's not a real thing, just something from a TV show; regardless, that is what a dick in a box is.
Right, but you get very misleading impression if you try to treat a word used by a handful of people as a 'normal' word. If you adjust each one down 10000x to factor in how many people would actually use them then you no longer have this horrible distasteful revelation by reading urbandictionary. You only have a couple distasteful words, per region, but each region has a unique set.
