Come to think of it, I did once and I had only half-realised at the time. o_O I was browsing aimlessly as I am often wont to do, and a fairly strange individual had been lingering about nearby. I didn't pay him much heed before, but sci-fi has an armchair nearby and as I made my way to browse there there he proceeded to sit down and cough, loudly, every half a minute. I certainly noticed that. It was probably an innocent quirk or sign of a badly-handled illness, but did nothing to help settle my muffled suspicions.
I decided not to make eye contact and just finished up my browsing - it was near closing and so there were a few staff wandering about. I decided not to think any more of it - I prefer not to let my imagination run wild when I don't know something for sure - but I also forget how feminine (and how strange) I might look at times. Since people will either read me as a woman or a transsexual, I'm not in the best of camps. ^^;