Star Puffs, you need to calm down a little.
If you take it at face value and think that he indeed might not have known that you are female, then addressing an anonymous entity as 'sir' could just as easily be seen as a sign of respect and not an 'obtuse sexist gaffe'
...Because let's face it, amongst the ordinary folks just looking to communicate on things like 1:6 scale figures...or people like us, the 'net is also the headquarters of anonymous, armchair warriors. They thrive on the fact that a person can say or be anything without fear of discovery.
Everything about you screams "this person is female", but in a world of anonymity...that cannot be taken for granted. You should really be open to the possibility that you may have, on this occasion, jumped to an incorrect 'foregone conclusion.'
Oh good lord.
So let me get this straight, I made a snarky comment to defend an artist I like, and then took advantage of a mistake to further mock some poor observation skills on CollectorGuy's part. You and Rorywan in turn go into kneejerk defensive mode about remarks not even remotely directed at either of you.
...but of course in your minds I am the one who needs to "calm down"*. Me thinks the gentlemen do protest too much.