Funny / The Marriage of Figaro
The Count's reaction when the Paper Thin Disguises come off: "Oh God, now I'm confused."
Figaro, when told he is to marry Marcellina.
Figaro: You can't do it without my parents' consent!
The Count: Who and where are your parents, hmm?
Figaro: Give me ten years, and I'm sure I can find them!
If done correctly, the moment when the Count tries to pull his 'wife' out of her hiding place and first produces the rest of the cast who weren't on stage at the time.
The Countess's attempts to convince the Count not to worry about Cherubino's being in her dressing room, which actually make things worse.
Again, if done correctly, Susanna coming out of the dressing room and bewildering the Count and Countess can be side-splitting.
Aside from the usual Armor-Piercing Slap, Lisette Oropesa's Susanna straddles, elbows, and judo throws Figaro. Confirmed by the actress herself.
Cherubino being informed he's going to join the army in "Non piu andrai". Figaro keeps piling on the Rated M For Manly arguments (Marching! Glory! Explosions! Big mustaches! Fancy hats!) while Cherubino looks ever more horrified.