What do you get when you put a baby in a box filled with glass and nails and push it down the stairs?
... A boner.
Baby Downstairs
Explanation
Explain Bear
Alright listen up buttercup. The punchline is a play on words. The baby goes "bonk" when it hits each step on the stairs. But the joke says "boner" instead. That's what makes it funny (or not, you are the one who wrote it). You are welcome, dumb dumb.
A random passbyer
I don't get it sry
Anon
that was a roller coaster of emotions