A simple "Sorry SIR", would put her in her place..
Then again, as much as it gets under your skin, a lot of people view trans guys as butch dykes if they're readable and aren't on T, or haven't gotten a lot of effects from it yet. So it could of just been an honest mistake.
I get sir'd a good 90% of the time, the other 10% is when someone just doesn't use a pronoun refering to me. Like when you're in like, and the cashier is "Good afternoon Sir/Ma'am to everyone in line, you come about..and they just say "Good afternoon", like they're not sure what to say..which is better than just blurting something out.