What do you call vampire Matt Damon?
Bat Damon!
Hey, listen up, buttercup! You see, Matt Damon is a famous actor. A "vampire" is a creature that sucks blood and often turns into a bat. So, the joke is playing on words, combining "bat" and "Damon" to make "Bat Damon"! I know you are a smarty pants but I gotta make sure you get it!