So ah. Here are some tentative headcanons concerning Enjolras.
First here are a few that are just extrapolations of canon:
You know when he’s staring off into space while talking? Responding without turning to face you and such? - Yeah, well, people assume he’s being Aloof and Dramatic, but actually direct eyecontact makes him uncomfortable.
He doesn’t talk much, and when he does, it’s in short sentences - unless inspiration hits, and it’s about something he finds Important - then he can go on nigh indefinitely.
But these flights of the soul aren’t all that commonplace, usually he’s perfectly content to just listen to the others.
Speaking of these flights of the soul, after one of his big speeches (I think it was Love Thine Is The Future) when he falls silent those standing closest to him notice that his lips were still moving - that’s because he meant to go on, he did, but the words just wouldn’t come out.
He thinks and talks in strange metaphors - at least strange to others. Whenever he drops a random Latin phrase in a sentence that seemingly had nothing to do with what he’s saying, rest assured it made perfect sense to him. He just forgets his audience isn’t always following his inner logic.
He has an excellent sense of space - at the barricade it’s mentioned he was able to keep track perfectly of what’s going on at which point, able to visualize the whole thing. (He’s excellent at navigation, Combeferre can correct the dictionary, Enjolras can correct a map.)
He’s actually pretty tactile - but only with the Right People. (Marius never realises that he was one of these.)
And now for the pure, baseless headcanons:
He keeps his hair a lot longer than is fashionable. On one hand, it may be a tiny bit of vanity, but he also likes the feel of it. Both the weight and being able to play with it. If it were cut, it would bother him terribly.
On the rare occasions he actually makes it into bed he likes to wrap the blanket around himself as tightly as possible, and to squeeze into the corner made by the bed and the wall.
(…It’s probably not that much of a stretch to HC him as autistic, is what I’m trying to say.)