Chin

"Forget Mudflap's jaw. Check out the asteroid-sized chin on sarge"

"YOU GOT A COMMENT, FUNNY BOT?."

- Bumblebee and Sentinel Minor

A chin is the lowest part of the jaw on creatures with mouths. Transformers have had chins since as long as they've had faces. Why is something of a mystery, since Transformers do not technically need mouths (and some don't). One must also ask why certain bots have such large chins when they don't actually need them. Humanization? Experiences with mammalian lifeforms? Only Primus knows the truth.