Anyone who can get a girl to enroll in this class gets extra credit.
That makes me feel uneasy.  Are you saying that you want more women in the class to look at?  Or is there another reason?
No of course not. It's just the joke.
Making jokes that are sexual in nature are inappropriate for a college classroom.  It is both off-putting and wrong to be making creepy comments about women. Especially as a person in a position of power.