What's Everyone's Favorite Mini-Trope?

I'll go first. Mine's the one where 2 characters are professors or teachers of some kinda of university or other place of secondary education and to students seem vastly different. These total opposite educators, one beloved and the other not so much, both have 1 thing in common. They both have a spouse whom they describe to be they're perfect match. The Sunshine professor describes their partner as kind, loyal, and caring. While the Grumpy professor presents their partner as intelligent, blunt, and unbashfully confident. "Oh how difficult these 2 people and therefore their partners and relationships must be," say the students none the wiser. But oh how wrong they are. By some silly room stumbling or sneaking around, the teachers are found out to be sneaking around, perchance frenching it up!!!??? "How could they!" The students exclaim. Their partners that they love so dearly, oh the humanity! Teachers are shunned for infidelity. They wonder why, some kid slips up, and they find out. Teachers reveal that actually they've been the others dearly beloved all along. Hug, kiss, shocked faces all around, rinse and repeat. It is my guilty pleasure. If I was to guess, I'd say I've read at least 40 of these and I hope I'll get to read 40 more. Its predictable and so fun and can fit in with pretty much any fandom as a one shot. To whoever came up with the original concept, I hold them responsible for many a sleepless night.