I'm completely with you on Snape and Potions, but a reluctant DADA teacher Snape who just wants to get back to his cauldrons would be pretty funny.

Dumbledore: "No, Severus, you may loathe all that foolish wand-waving as much as you like, but Potter didn't make the Advanced class in Potions, and you need to remain his teacher. I'm afraid it really can't be helped, dear boy - you're needed there."

Snape: *loathes Potter more than ever and plots to have him killed by a little something in his pumpkin juice*