I heard a version that the teacher was showing little kids pictures of animals and asking what each animal was. She showed a picture of a steer and one of the kids said, "It's a cow!" The teacher nodded and showed a picture of a goat, and one of the kids said, "That's a billy goat!" The teacher smiled encouragement and showed a picture of a stag. The kids were puzzled, and stared at the picture. The teacher offered a hint, "Your Mom might call your Dad this sometimes." And one of the kids proudly exclaimed, "It's a horny bastard!"

It IS to laugh!