It stands to reason, Clint thinks, as he twists himself around to get a better look at his ass, that he'd get a soulmate mark in such a stupid place. At least he can be sure that no one will see it accidentally, unless he starts sleepwalking naked (he resolves to start wearing boxers at least when he's asleep) or if he's injured too badly to stop them looking (that one he can't prevent).

It's not until Bucky slaps him on the ass one morning as he walks past that his skin feels like it's on fire, and he realises that soulmate marks can be activated without skin-on-skin touch; apparently the tatty old sweatpants are thin enough that it still counts...