"Stunted Growth" joke

A young couple had been married for a couple of weeks, but the man was always after his wife to quit smoking.

One afternoon, she lit up after some love making, and he said, "You really ought to quit."

She, getting tired of his nagging, said, "I really enjoy a good cigarette after sex."

He replied, "But they stunt your growth."

She asked if he ever smoked, and he replied that he never had.

Smiling and lifting her gaze to his groin, she said, "So, what's your excuse?"