This husband and wife were in their room one night, having s*x.
He had her up on her knees, and he was standing behind her, banging her from behind, when their son walks in.
The kid looks, turns around and storms out of the room.
Obviously, the wife stops and is worried about the boy, and tells her husband to go talk with him, to be sure he's ok.
The husband says, "oh heck, he's a boy, he's fine."
Few days later...
The husband is in the kitchen and hears a noise upstairs, lots of banging and screaming going on so he goes up to check it out.
He opens his son's door to find that the son has his grandmother, on her knees, and he's banging her from behind.
The man yells, "Boy, what on earth are you doing??!!"
The boys says.......
"Not so funny when it's YOUR mom, is it?"