Oh, I’ve got plenty of that! ;o) Here we go…
Give me a character and I’ll tell you my headcanon for:
What they smell like: Steel and rawhide and oil. Rich and heady and musky and sensual.
How they sleep (sleeping position, schedule, etc): He tries to sleep flat on his back, mostly - in my head, it’s because he doesn’t like being caught unawares - but he tosses and turns a lot and often ends up on his stomach. He doesn’t usually sleep well. He’s a restless sleeper, and he has a hard time shutting his brain off. He’s also an early-riser, though, and he gets annoyed with people (ahem…Allan) who feel the need to sleep later/more than he does. (Seriously, Allan’s always napping, and it’s one of headcanon!Guy’s biggest pet peeves.) ;o)
What music they enjoy: He likes classic rock, but he also has a strong penchant for metal. (I mean, how could he not?) Led Zeppelin. Metallica. Iron Maiden. Judas Priest. Black Sabbath. HIM. Linkin Park. (You get the picture.)
How much time they spend getting ready every morning: He’s a tad on the vain side, and he definitely dresses to impress (mostly for Marian’s benefit), so he probably takes a bit longer than most to get ready in the morning. His hair certainly takes some work.
Their favorite thing to collect: Weapons. He likes to pick up unusual daggers, etc. that he comes across in his travels (e.g. the thin, curved dagger he stabs Marian with, probably acquired in the Holy Land).
Left or right-handed: He’s right-handed. He holds his sword with his right hand, and he shoots right-handed (left-eye dominant).
Religion (if any): Christianity…but, like so many others, only really by default. He goes through the motions, but it certainly doesn’t dictate his moral code or influence his actions much. He does start to pay more attention to the implications of his religion toward the end, though, as he struggles to come to terms with his regrets and seek redemption.
Favorite sport: For some reason, fencing comes to mind. That’s a rather amusing mental image, but I think it’s because he’s a very schooled and sophisticated swordsman. He has impressive form, footwork, and reflexes (he’d have to be, being Master at Arms and all) whereas the outlaws’ sword-fighting styles tend to be driven more by brute force, tenacity, and sheer necessity than anything else (although Robin is more skilled, having had proper training).
Favorite touristy thing to do when traveling (museums, local food, sightseeing, etc): I kind of see him as being something of a museum-goer, but exhibitions of historical artifacts (especially weapons and armor), not art. War museums, that sort of thing.
Favorite kind of weather: He likes a bit of overcast and drizzle. Brooding weather definitely suits him best!
A weird/obscure fear they have: Fire. I have this headcanon that burning down Marian’s house at the start of S2 to “get back at her” for humiliating him at the alter was, in his mind, one of the worst things Guy possibly could have done to her, because of the childhood trauma he suffered - losing his home and his parents - due to the fire at Locksley Manor (which he feels personally responsible for). He wanted Marian to feel the pain he felt, watching her home burn with the knowledge that it was, in a sense, “her fault”. When Robin sets Guy on fire in his armor in “Childhood”, all headcanon!Guy can think about is his parents burning alive in the house fire. When Robin cracks open the vat in “For England…!” and sets fire to the oil leaking onto the ground to help the outlaws make their escape from the castle courtyard, Guy reacts by backing away and shielding himself from the heat. Byzantine Fire scares the hell out of him - while at the same time having a sort of morbid appeal - and the incident with the barrels of black powder exploding and almost killing him is really traumatic for him as well. (Even more interesting, then, that it should be Byzantine Fire that kills Vaisey and Isabella in the finale.)
The carnival/arcade game they always win without fail: Guy turns up his nose at carnival/arcade games. They are completely and utterly beneath him. He’d probably just stand there and watch everyone else making fools of themselves, smirking the whole time. ;o)