For someone who aspires to be an Olympic class insulter, Marty seems to be having trouble even getting picked for the team. It's his sad lack of imagination combined with his complete ignorance of what constitutes a really good zinger.
Simply making up stuff about the target's personal hygiene or sex habits (which may tell you more about him than it does about the person he's trying to insult) and combining it with feminist, ageist, or other stereotypes liberally mixed with juvenile crudeness just doesn't cut it. The trick is to find out something that is actually true about the target, and then put a spin on it that's funny enough to get everybody else to laugh. A good study of the "nose" speech in the first act of Cyrano de Bergerac: ". . . these things and much more you might have said if you had any touch of letters or of wit to color your discourse, but of wit, you never had an atom, and of letters, we need but three to write you down. A-S-S!"
But then, Marty is laboring under great difficulties these days. He's upset because that Chicago red-hot he prizes so much is all shrunk and wrinkled, his buns have gone soft and soggy, and he's all out of mustard.