A few times...
Fairly early in my transition, I was at a costume party. This was after about 2 months on Hormones. and I was not out. For whatever reason, I decided to go as myself, blonde long hair wig, dress, heel boots. many people - who knew me from earlier that day when I helped set up the party - did not even recognize me. I was dressed for a party but not in a costume.
Long story short, a few hours into the party, some drunk guy walked up to me and blurted out: "Are you transgender?" which really knocked me off my heels. Initially, I had no idea how to respond so I just danced around the topic. Tunes out, his sibling just came out as mtf and he was sensitive to the topic... Lucky enough, no one heard it and the guy was drunk enough that he will have forgotten about it by the end of the evening.
One lady at one of my customers suddenly complimented me on my boots... yeah, female boots and she knew right then but kept it to herself.
The most recent was through a picture on social media which some of my wife's coworkers saw. Apparently, it was a "hot topic" at work for a few days. Of course, they looked deeper and found my gender set to "female" too...
I did get the "are you a boy or girl" question a few times. Usually, I do just respond by asking what they think. For the most part, they get it right but one kid was insisting I am a boy due to my voice. I was puzzled and stopped responding, now I would just say my voice is sick.
While I got outed, so far the consequences have been limited.