So, me and this girl I talk to where leaving University and going to the bus stop together. I got lost in thought at one point,thus staying behind and her opening the building door.

Then she says "The door's quite heavy. Aren't you supposed to open it instead of me"

I actually said nothing as if to ignore it. Could her statement be anything beyond face value? I thought about a comeback. "That would be sexist". Was I correct not to say it?