Hey, first time posting! A few of these I may end up housing myself, but in case anyone else is interested in taking them in:
1.) Something I find interesting about the bios in the series production bible is that Ratchet's function is listed as "Mechanical engineer", same as Wheeljack's, while First Aid's is "Doctor" and even Hook's is "Surgical engineer". In the same vein, Ratchet's "personality" is given as "repairman" and his bio emphasizes his ingenuity and engineering expertise before his ability to fix fellow Autobots. I know, I know, the bios say a lot of things, but this is where my interest is caught. So!
1a.) Let's say Ratchet was an engineer before he was a medic. When did it happen and how does he feel about it? In a universe where he lived to see the end of the war, would he maintain his status as a medic or set up shop as an engineer?
1b.) Hook absolutely freaking hates him for having a better reputation as a medic than Hook himself does because, as far as Hook is concerned, Ratchet isn't a proper medic to begin with. Heck, maybe he's not even wrong-- maybe Ratchet doesn't have medical certification.
2.) Ratchet's portrayal in fanon is often downright abusive, a far cry from his cartoon portrayal (or any other canon portrayal of him I've seen, tbh, but I haven't seen everything, so *shrug*). I'm amused by the idea of this reputation being something he's cultivated without meaning or wanting to. Suppose several people have witnessed him backsassing Optimus and threatening to shut Ironhide up by force, perhaps not realizing that they're both friends of his. Suppose several people have caught him when his temper was frayed and he's swearing the air blue about how all he ever does is fix people who go out and get busted up again pulling ridiculous stunts. Suppose several people have witnessed his technical expertise, whether it's some gadget he's helped develop or some weapon improvised out of spare parts on an active battlefield. Suppose it all comes together...
2a.) Everyone tells the new recruits horror stories about Ratchet, who will snap at the drop of a pin (no, really, someone dropped a pin in his presense once and was never seen again) and reformat unruly patients into medical supplies (or maybe the pin-dropper was seen again... as a repair sled). Every little thing he does gets exaggerated by the masses. Scolded someone for taking a careless risk? No, no, you mean he launched into an hour-long rant that left three people in stasis. Waggled a wrench at someone while insisting they accept pain inhibitors? Oh, you mean (one of) the time(s) he bludgeoned someone into unconsciousness because they wouldn't shut down for surgery. Told the Prime to go recharge? Man, you should've seen him drag the Prime to a recharge chamber by his antenna.
2b.) No, really, everyone tells scary Ratchet stories. Yes, Decepticons too. And since Decepticons aren't in position to get to know Ratchet personally, the belief in these rumors persists much longer and among more people. And since everyone knows Autobots are all soft on each other, how much worse must he be to Decepticons who fall under his hands? Facing him on the battlefield isn't so bad-- he's a decent shot and you might even find yourself getting jumpkicked, sure, but he's no true warrior-- but you never want to find yourself looking up at him from one of his tables. Decepticon POWs are actually among the most cooperative patients he deals with, because they're that much more afraid of his infamous temper and cruel skill. Maybe Hook even threatens to send his own difficult patients over to the Ark, if they're so disdainful of being in the Constructicons' care.
3.) After hearing him grumble so much about all the work he has to do, people generally assume that Ratchet would prefer to be left alone to get said work done. When he's not in the repair bay, he's in the labs. Rumor has it he used to love a good time, but those days must be long past. He never makes an appearance at movie/game nights or the occasional parties... The perhaps obvious twist is that he's never invited and may not even be aware of these events until they're well over. Most or even all of them are scheduled during his duty shifts anyway (since no one expects him to be interested in attending). This doesn't have to happen more than a few times before he's convinced that he's unwelcome there.
3a.) Someone decides to go out on a limb and ask him along. Whoever it is doesn't actually expect him to say yes, and so is utterly unprepared for how eager he is, never mind how happy. It's possibly a little awkward, since this someone assumes that it's him (or her?) that Ratchet is so excited about.
3b.) Alternately, Ratchet and someone or other have gotten flirty lately and he's anticipating this someone asking him to one of the few events he's aware of in advance. But everyone knows that's not Ratchet's scene anymore, right? So his new paramour doesn't bother. As for why Ratchet doesn't just ask himself, doing so feels wrong when he's so clearly not wanted at these events on his own. Or even as a plus-one, apparently.