I know what you are

Little Johnny wants to do it with his teacher but she always refuses.
One day, finally he suggests "Ok how about if I gave you $1 million,
would you do it?"

The teacher, in an attempt to end it all replies a bit amused "With a
$1 million? Sure I'll do it with you."

Little Johnny: "How about for 50 bucks?"

Teacher: "Hold it there young man what do you think I am?"

Little Johnny: "I know what you are. I'm just bargaining on the price."