What animal has the most disgusting defense mechanism?
My personal favourite is the sea cucumber
Well everyone knows skunks can produce a rather foul smell, but my favourite defense mechanism belongs to the Sea Cucumber which ejects parts of its internal organs - including its intestines, various blood vessels and small bits of gonad (sea cucumber internal private parts) - through its cloaca (a sort of multi-purpose orifice/hole used as a mouth, anus and anything else that needs a hole). This process actually causes the cloaca to tear a bit too.
This is to try and surprise its attacker so it can escape. I can't speak for all sea creatures, but having someone's internal organs ejected into my face would probably surprise me.
For a hilarious video on the topic, I recommend Zefrank's true facts about the sea cucumber (type it into youtube).
Hope this helps!