So here's the lesson for next time:

The only person who can do anything about your brother's behavior is you.

There's a reason everyone was frosty. Yes, your brother is an asshole. But when it came down to whether or not you - the person who knows him, who was clearly aware that he was an asshole - were going to do anything about it, the answer was NO.

It's your job, as your brother's keeper, to be a buzzkill in situations like these. It is necessary to chastise him for his behavior in places those who are offended can see. This is why parents make their children apologize to the old ladies that get trampled in exuberant cases of tag or red rover.

As members of the service industry, bartenders - as cgod pointed out - must deal with assholes on an hourly basis. My seven years in clubs taught me that those in the service industry appreciate it when they do not have to go it alone. While you weren't condoning your brother's behavior, you weren't exactly condemning it. If it's any consolation, the grade of assholery committed by your brother is pretty much misdemeanor territory... but that also means that you didn't really face any penalties for keeping him under control. I don't know if there are any service staff left who do not know Swanson's #32 - a person who is nice to you but is rude to the waiter is not a nice person. Condoning rudeness is rudeness.

One other thing - even if you had been hitting it off gangbusters with one of the bartenders, the likelihood of anything happening was nil. Bartenders date people who aren't bartenders all the time but I never met one who dated a customer they met while working. However, had you done the right thing and shut your brother down on the spot, she probably would have remembered you.

This probably reads like I'm coming down on you like a ton of bricks. I'm not. I'm trying to make clear that you feel bad about this because you feel responsible and you're trying to figure out how that could be. Here's your answer - by not shutting him down where he could feel shamed in front of others, you're risking the possibility that he'll do it again. You banked immediate uncomfortableness so that you could withdraw it (with interest) next time.

And there will be a next time. And when it happens, it's your job to say 'Hey, bro? Seriously not cool. You can either shut the fuck up about the bartender or you can walk home. By the way? I'm tabbing out and you're buying the rest of the drinks in this place and you're tipping heavily or I'm going to tell her that you wet the bed until you were eleven."

And every time you do that it gets easier and easier and easier and before too long, you're no longer victimized by the asshole behavior of others around you because you've long since learned to shut that shit down before it becomes a problem.

God speed, good luck.