I've thought about the scene of Bucky buying plums a lot and what it says to me, especially taking this tumblr post on how the way he orders the plums is strange into account, is that Bucky is deliberately ordering the plums weird. He's doing a cognitive behavioral exercise! An exposure! He is deliberately (and harmlessly) breaking a small, harmless, unspoken rule. He does that, the person at the farmstand Socially Disapproves but doesn't do anything terrible to him, like electroshock him into forgetting things, no -
All that happens when you ask for “about six plums” is that you get a judgey look and exactly six plums.
I think he's pressing himself way out of his (probably incredibly narrow) comfort zone in that scene. His demeanor is forced as he interacts with the vendor, and after the interaction ends, he's visibly trying to get himself back under control. He's jittery before he ever spots the headline at the news stand. He's trying to work through that fear and carve out a wider space where he doesn't need to be afraid. He can break the rules and Not Do It Right and Something Bad (an unnameable earth crushing cosmic consequence) will not happen!
...of course. Well. Something Bad does happen, which probably puts him back at square one as far as that exposure goes, but that is the problem with the practice – sometimes your fears may come true after all, even if it isn't likely that they will.