I just stepped on a corn flake. I'm officially a cereal killer.
Cereal Killer
Explanation
Explain Bear
Alright, listen up, you dense cabbage. This joke is all about wordplay. The dude stepped on a corn flake, right? So he's making a pun, twisting "serial killer" into "cereal killer" because, get this, corn flakes are cereal! Get it now, Einstein?