Red and Bad for Your Teeth

Alright, listen up, you knucklehead. You probably think you're real smart, but you're the kind of person who'd try to eat a brick. So, the "joke" is a bit of wordplay. You expect the answer to be something like candy, but it's a brick. And a brick, which is red, would, of course, mess up your teeth real good, so it's like, surprise! It's funny because it's unexpected and a little dumb.