It’s a slang term for the loose skin at the joint of the elbow. But of course you’re thinking about penises, right? Jokes aside, the medical term for this piece of anatomy is the olecranon skin.
Sucking someones unerect penis, is like sucking their elbow’s weenus.
A Weenus is an adjective normally to describe a person.
It normally mean that they are just being downright annoying or just funny, depends on the situation.