One night, a horny old geezer decides to get himself a hooker.
Since the man doesn't have much money, he looks for the cheapest whore in the nearest Red Light District. A short while later, he finds what he's looking for and spends $10 for oral sex and intercourse.
The next morning, the old geezer wakes up and discovers he has crabs. So, he gets dressed and heads down to where he had been the night before. He notices the same hooker on the street corner, so he marches over to her and says, "Hey, lady, you gave me crabs!"
The hooker replies, "Hey, old man, what did you expect for $10? Lobster?"