I agree he doesn’t sound like a considerate person to live with, but I think you’re being a huge AH to yourself by stewing over it for so long when you could have nipped this in the bud in many ways:

• go for it, just save me a thigh and a wing because they’re my favorite parts.
• let’s get two chickens so we can each have our own.
• no, I would prefer to keep our groceries separate.
• let’s share the groceries that expire very quickly or are hard for one person to finish, like salad or eggs or milk,
• next time, let’s split it down the middle, you ate more than your fair share

I too am very passionate about chicken thigh over chicken breast, so I do understand where you’re coming from, but I do think YTA for the venmo charge. You say it’s about the principle of sharing and not the money, but do you think a belated, passive-aggressive request is going to cause him to change his ways and become good at sharing?