Long emotional abuse over his chin may have made Sentinel the jerk he is today. Or he was just built that way. Or maybe he's just annoyed because Bumblebee mistook him for Jay Leno.
- "Forget Mudflap's jaw. Check out the asteroid-sized chin on Sarge."
- ―{{{2}}}
- "YOU GOT A COMMENT, FUNNY-BOT?!"
- ―Bumblebee and Sentinel Minor[["Autoboot Camp"| [src]]]
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 even have one). One must also ask why certain bots have such large chins when they don't actually need them. Humanization? Experiences with mammalian lifeforms? Required for socially acceptable chin-stroking when plotting? Only Primus knows the truth.
It is worth noting that prior to Animated, many of the Transformers had triangular or rectangular "beards". Megatron had originally lacked one but after being reformatted he too received a beard. This is most likely due to the Japanese origins of Transformers, which makes them fairly consistent with every other typical robo anime.
It may also be worth noticing that most Animated transformers also haven't got Noses or sometimes even faces and yet still manage to have a big Chin.