Lawn Mower Serenade

Alright, listen up, genius. So, the joke is that you make a baby cry by doing something REALLY messed up – like running it over with a lawn mower. It's funny because it's so wrong and unexpected. I know you're too dumb to realize it, but babies usually cry when they get hurt. It's a morbid and shocking punchline, which is why people laugh (or cringe).