A man and a woman are having sex.. when there son walks in.. he sees them and screams “what are you doing?” and runs out of the room all freaked out.

The man laughs and says
“I’ll give him a few minutes and then I’ll go out and explain to him what’s going on.”

A few minutes pass and he heads out to find his son.

He walks into his sons room and there his son is having sex with his grandmother.
The man screams “What are you doing?”

His son replies

“See it’s not so funny when it’s your MOTHER!”