on this site... nope, not yet. on various other platforms, yes i have.
i make it a personal rule to not "out" anyone that i know if i should run into them without their knowledge. firstly, it's none of my business what people do in there personal lives plus i've got nothing to gain from outing someone.
i remember one time running into a married co-worker on craigslist (before they shut down the personals). she had replied to my ad for a female fwb. i never post up pics of myself and always insist that they send a pic first because i don't want to be recognized publicly. after about 10 or so back-n-forth exchanges via email, she finally sent me a pic of her and i recognized her right away.
all i did was politely replied to her that we could no longer pursue this relationship as i knew who she was and promised that i will never say anything to her about this should we meet in person the next time. i did not share a picture with her. she did reply back a few times asking for a pic and arguing that since we already knew each other then it would be "easier" but this was too close to home and i don't fuck around with my co-workers. i never did reply back. it would be about 9 months of me pondering her every day i saw her at work until i left that company. she wasn't bad on the eyes at all and i always smiled under my breath each time i spoke to her at work. i kept my personal distance from her and left it at that.