I can't think of an incident where I have. But I probably have. Fag or not, I'm a white male. I'm sure my very existence is a microagression.
Seriously, though, yours wasn't really a microagression unless you were ignoring the woman because she was a woman. If you were ignoring her because you had been dealing with the old fellow and had just continued that, it may have been a little unintentionally rude, but it wasn't a microgression. At least not to my mind. But who knows? Most of the concept of microagressions is booshee.
-Samantha Jones, SatC