Hmm... this one will be tough for me. I'd have to go through all of the shows I really love and narrow it down...
Ranma 1/2 - Ryoga sees boobs...
Slayers - Fish version of Jerry Springer...
Blue Seed - "Oooh! Rabbits, today!"
El-Hazard - Feel better...
Project A-ko - The very last ending scene
Maria-Holic - "I'm back, Master."
Haruhi-chan - Halloween ninja vs. Santa... ninja...?
Ninja Nonsense - "Oops! My hand slipped..."
...I'll stop there...
Ranma def. Ninja...
Slayers def. Haruhi...
Maria def. Blue...
El def. Project...
Slayers def. Ranma...
Maria def. El...
The entire episode in The Slayers where the lady fish claims to have had two kids with Gourry, and the daughter falls in love with Zelgadis, who's Gourry's... son...?
So much "WTF?" in that one...