The barman may have been told by another member of staff not to serve someone who resembled you - I've seen this happen in action, and sorry but most people do get shitty with the staff when refused for any reason at all.
They can be the most reasonable person in the world, but refuse to serve them and it's like the sky has fallen in. The entitled attitude towards alcohol is disgusting in some people, it really is, especially considering they don't carry any of the concequences of an illegal sale, that's all for the person serving (unless it's a proxy sale, but the server rather than the buyer is more likely to get done, and more harshly)
It's not beyond the realms of possibility that he just 'took against you" no, but if he was serving other women then I don't see how you can feel it's because you're a woman.
I've been on the recieving end of complaints that are unfounded, because a customer couldn't get their alcohol, the trump card is "Well she was rude"
Of course he may have form for this and if he does, and if he was genuinely rude, then a disciplinary is what needs to happen.
However having been in the industry a long time, I'd be more inclined to think that you were refused alcohol service and took offence, which you displayed, which led him to refuse all service. Then you say he's rude.
If he'd served you and it turned out he was right not to, he gets a roasting. Lose lose for the bar man either way isn't it. Dare say his version of events differs to yours, but of course yours will be believed because you're the customer.
In general it boils down to the fact people don't like being told no by those who are serving them. Well unfortunately the law charges those people with upholding the rules it's made, with harsh penalties if they don't.