Because it will go right over his head
When talking to you, the extrovert mathematician looks at *your* shoes.
If I've told you n times, I've told you n+1 times...
Because she had a pun in the oven!
An unfunny joke
Because their heads are so far from their bodies!
A 20 dollar bill
A nearby horseman answers, "Ooh! Ooh! I know this one!"
Just a little