"The Gambling Problem" joke

Little Johnny likes to gamble.
One day his dad gets a new job so his family has to move to a new city.
Johnny's daddy thinks, "I'll get a head start on Johnny's gambling."
So he calls the teacher and says, "My son Johnny will be starting your class tomorrow but he likes to gamble so you'll have to keep an eye on him."
The teacher says OK, she can handle it.
The next day Johnny walks into class and hands the teacher an apple and says, "Hi, my name is Johnny."
She says yes I know who you are.
Johnny smiles and says, "I bet you ten dollars you've got a mole on your butt."
The teacher thinks that she will break his little gambling problem so she takes him up on the bet.
She pulls her pants down and shows him her butt and there was no mole.
That afternoon, Johnny goes home and tells his dad that he lost ten dollars to the teacher and why.
So his dad calls the teacher and says, "Johnny said that he bet you that you had a mole on your butt and he lost."
The teacher says, "Yeah, and I think I broke his gambling problem."
Johnny's dad laughs and says, "No you didn't, he bet me a hundred dollars this morning that he'd see your ass before the day was over."