So I don't know if you've seen it but skin wars is a body painting competition (it's on netflix very fun to watch). But now imagine R the body painting artist being paired up with model Enjolras for a challenge and all he can say is "holy shit fuck me"
(Oh my god I need to watch that, fantasy makeup design is one of my hobbies!!)
This is actually such a great headcanon though, because i can tell you from personal experience that something as up-close-and-personal as having your face (let alone your entire body) painted by someone you’re attracted to–or being the artist–is incredibly nerve wracking and awkward and just a little exciting.
I think that, although the usual slightly antagonistic/politically flirtatious dynamic would still be there, Enjolras would definitely be very excited to have Grantaire use him as a model–strictly because his art is so beautiful, of course. It would be kind of cool to have Enjolras as trans man for this as well, and R constantly telling him how wonderful his body is despite the fact that trans men aren’t exactly seen as ideal candidates for any sort of modelling.
I imagine R doing something like this, with Enjolras as a stained-glass image of Apollo: