This old couple was sitting in their rocking chairs on the back porch when the old lady reached over and knocked the old man out of his chair.

The old man got up, sat back down in his chair and said "What was that for?"

The old lady said "That was for 50 years of bad sex."

A couple minutes later the old man reached over and knocked the old lady out of her chair.

She got up and said "What was that for?"

"That's for knowing the difference."