fbil hasn't earned Best Man Position

I feel like ultimately FH’s call. I would assume he will still want him in the wedding party but not as Best Man!

You're allowed to feel however you feel, but it's ultimately not up to you who your FH has as his best man.

You can feel however you want to, but your fiance gets to choose whomever he wants.

There’s a lot of dirty laundry here that has absolutely nothing to do with his role in the wedding.
His status as best man or not should be fully up to your FH, and based on their relationship entirely. If FH doesn’t want him to be his best man because their relationship is tumultuous— that’s absolutely fine. If he does still want him there because he’s his brother and it’s just what he’s always wanted to do— that’s fine too. I would manage expectations from him (maybe mention to another groomsmen that he shouldn’t be left alone in charge of the bachelor party), but that’s fine. The best man doesnt *have* to give a speech. You could skip it altogether or FH could ask a closer friend if he wanted to. No big deal.

It’s okay for you not to like your husband’s brother because he is a difficult personality or a different lifestyle. But it’s not okay to interfere in your husband’s relationship with him. Just be civil and keep interactions to a minimum. If he ends up best man, it shouldn’t really affect your end of the day— it’s really just a few pics you’ll have to suffer through together.
I also don’t think anything about his actions read as intentionally disrespectful *toward you* . He sounds like an inconsiderate person, sure , but, it doesn’t sound personal. Just sounds like who he is. He may grow up or he may always be that way, but he will always be in your husband’s life, so you will have to put up with him— so I’d try to learn to shrug him off a bit, not take his behavior as a personal offense and just that his personality and behavior isn’t on par with yours. He has bad manners. It would be great if he changed, there are some things you could ask for when you’re together (“hey if you’re staying here, can you do dishes?”) —- but this stuff shouldn’t play into the bridal party, and is a separate issue. I’d still personally step back and let FH make his own decisions about his groomsmen. Seems like he recognizes his bro’s flaws but is still considering him, so if he wanted him up there, it’s probably something that is deeply internally important to him. I wouldn’t get in the way of that, regardless of how I felt about him and his behavior.

Who is a best man or groomsman is 100% your fiance's decision. I'd deal with the deeper issue first, your FBIL's lack of respect for you & your fiance and how you both will deal with that going forward and having a united front.

This is not your call--FH should choose who his best man is. If you feel that he's been blatantly disrespectful to you, have spoken with FH about this, and he's deciding to include him as best man, then that's a problem between you and FH you'll need to address.

Small pet peeve of mine: no one "earns" a title like maid of honor or best man, it's just the person with which you're closest.