Maybe pro nouns should just be banned for the sake of political correctness. I totally get that a transgender person from whatever side of the fence would be offended when they are addressed opposite of their brain sex but short of having it stamped into your head or maybe wearing a hat proclaiming I'm a f**king Girl OK! The general public at large will not be aware of the distress it can cause when they get it wrong. I was out with a friend of mine, a trans female and she was sir'd a couple of times by the same shop assistant. I really felt for her and it annoyed me almost to the point of violence. To me it was obvious that she is female and in my mind he was doing it deliberately to cause offence. If I'd have known this for sure I'd have dropped him where he stood. Why couldn't he have just said "can I help you?" Why did he feel the need to add sir, it just isn't necessary. I'm almost ashamed to say I actually considered going back into the shop once we'd left to show this inconsiderate scoundrel the error of his ways >:-)
Honestly, I think you're blowing this up a little out of proportion. While I agree that pronouns are dumb in general, there's no reason to expect people not to use them. It should only be offensive if they get it wrong when you think you pass, but before then, just ignore it. No need to get violent.
The majority of people address others based upon how they appear, and likely do it without consciously being aware; pronouns typically come naturally. Look like a guy, addressed as so. Look like a girl, addressed as so.
Despite what may seem obvious to you that should indicate what someone wants to be called via pronouns, with more and more people appearing androgynous, it's entirely too difficult to really know without actually being told.
However, yes - perhaps the person could have simply avoided the pronouns altogether, but when I used to work at a retail store, it was part of our directives to use sir and ma'am when speaking with a customer at all times unless the customer specifically requested otherwise.
Whether or not this person was deliberately using the pronouns is unknown; but until it is known, I see no reason to become upset. I hate being called sir, but I understand why others do it. I look like a guy, thus - common sense.
No one can read another person's mind; speak up or let it go.