After making love, my wife looked at me disgusted and slapped me across the face

Shocked, I said "What the hell was that for?!"

She said, "That's for 40 years of bad sex!"

I slapped her, and she said,"What was that for?"

"That's for knowing the difference!"

As relayed to a coworker of mine when asking an older coworker for wedding advice upon the occasion of his upcoming wedding this week.