What does the word 'fully' mean as a noun?

Solution 1:

In contrast to deadrat's answer 'Fully' can be used as slang term for a fully exposed breast popping out (and possibly that breast being large or 'full'). Hence Dave Chappelle's use of the phrase 'Now that's a titty', the guys aren't just commenting because it's any old side boob shot or partial slip but the fact that it is a full blown exposed breast. That being said, I also think out of context the term can mean you fully agree with a statement or point of view etc.

Solution 2:

This occurs during a fight scene in which one of fighters inadvertently exposes one of her breasts. One actor comments admiringly "Now, that's a titty!" Jim Breuer says "Fully, man," meaning that he completely agrees with the assessment of the sight or that the exposure is complete or both. Likely, what he means to say next is "That is an official titty," but he's a stoner so his drugged-out verbal faculties substitute the last word he said that ended with a "y." And it comes out "That is an official fully."

It probably makes more sense if you watch the movie stoned. In that state, it's also likely that the movie will strike you as amusing. These are two powerful arguments for just saying "no" to drugs.