Just give me post CATWS asset being a little shit when he comes to live with Steve. Maybe he refuses to use a toilet and shits on the floor. Maybe he scowls when Steve tries to make him eat solid food and will only drink protein shakes or juiced veggies. Maybe he only eats Oreos or things Hydra never let him have but it makes him puke. Bucky doesn't want to shower or wear clothes. He likes to roll around naked or only wears sweatpants all the time. He refuses to get dressed just because people are over. Just general misbehavior and noncompliance for the sake of noncompliance.

Hydra's way of curing this behavior was obviously pain related.
So maybe while interrogating a Hydra agent, they happen to mention that Bucky's handler was also his 'daddy' and that spankings would usually help.
They just don't mention that spankings also turn Bucky on and mean that it's time to be a good sexy boy for his handler.

+Steve being so fucking frustrated with Bucky's behavior that he finally just breaks down and decides Bucky needs a spanking.
+Steve being all dad like and gentle about it. "This is going to hurt me more than it will you."
+ Steve with his hands full of horny, pliant, wiggly Bucky
+ Bucky calling Steve 'Daddy' afterward and being well behaved.
++ Steve's general mortification and angst for Bucky clearly having been abused and the worst part is that it actually improves Bucky's behavior and now he EXPECTS Steve to continue it.