The Asset messes up BAD and everyone's beyond pissed at him. Say he refused an order that fucked up a mission, or went AWOL, or ruined a trash party by fighting back. Gang rape is common for both reward and punishment but this time it's beyond the pale. They rape him so violently (and probably also beat him, electrocute him, etc.) that he literally dies...only briefly, because they revive him. He spends the rest of that activation period terrified and highly obedient.

Bonus round, if you want to bring it into the recovery stage: Bucky is sex-repulsed but tries not to let on because he wants so badly to move on with his life. Unfortunately flashbacks don't ask for permission and don't care which role he's taking (i.e., no, "just stick to topping" isn't a viable solution). An optimistic ending for him & his partner--preferably Steve--would be great, but don't make it easy on him. ;)