The Story of Sentinel's Chin - tfa
Chat, I have a headcanon. 'Tis a very considerable one. I have a headcanon that Sentinel originally didn't have the fat stupid chin he's known for now. He manually screwed it onto himself (hence the big screw thing in the middle). The reason for it is because he has a resting glitch face and everyone was terrified of talking with him because he always looked like he was on the edge of committing homicide. Of course, Sentinel had absolutely no idea until Elita-One told him.
So, the event and origins of it go like this:
Sentinel: Why does no one talk to me?!?!?!?1!?!1
Elita, trying to suppress giggles: Maybe it's because you look like you want to kill them?
Elita: Yeah, Sen, you have a resting glitch face.
Sentinel, who does not know what an rgf is: WHAT?!?!?!?
Elita, turning blue because she's holding back laughter: Look, I got the schematics for a chin mod a while back. Why don't you wear that?
Sentinel, scoffing: How is a CHIN going to help me?!
Elita, shrugging in a way she thinks is mysterious: It's the Chin of Truth, Sentinel. Wear it and find out.
The next day, Sentinel puts on the chin and walks into his first class which he, coincidentally, shares with Optimus.
Optimus: What the Pit is that on your face, Sentinel?!
Sentinel, chagrined: Elita told me to put it on. Is it working-
Random mech 1: Oh, Sentinel! Hi! Uh-
he gets distracted by the chin and momentarily forgets his fear
Sentinel: WELL?! SPIT IT OUT!
Random mech 1: We need... blueprints for-
they finish their conversation in a fairly civil manner, though random mech's gaze keeps falling to the damn chin, entirely perplexed more often than not.
Sentinel, smirking: It's working.
Optimus, suppressing what he thinks could be either hysterical cackles or hysterical tears: ...Right.
Optimus: You planned this.
Elita is dumbfounded for a moment before she bursts out laughing
Elita: I didn't think he'd actually do it!
Optimus, wry: It's Sentinel.
Elita: All hail the Chin of Truth! Come on, praise with me Optimus!
(Optimus did, in fact, praise with her after copious amounts of Engex. Sentinel walked in on them, promptly got drunk, and joined in)
NOTE: Sentinel used to take off the chin in basic training. After Elita died, he saw it as her memory, in a strange, twisted way. He hasn't taken it off since.