I started volunteering with a group that hangs art in a hospital. About every 6 weeks we turn over a new show with about 80 paintings from local artists. It's a surprisingly large time commitment, much of it during the workday, so most of the volunteers are retired. (I'm the young blood - scary!)
I took some offense from remarks one of the older fellows made to me -- he was operating on a lot of sexist assumptions. Like ... my husband made the frames for my own paintings. (I paint as a hobby, and I build my own frames. I even have tools!) He assumed I was a lady of leisure, with lots of free time. (Nope, I still run a business.) There was something terribly patronizing about his whole attitude that I really took offense to. It was hard to put my finger on it. He was amazed that I took offense, genuinely surprised. I guess he doesn't encounter women like me very often in his world, or if he does, they suffer in silence.
He was operating from stereotypes. But I have to admit, I know almost nothing about this guy myself! I'm also operating on stereotypes based on his age and a few brief exchanges. Which may be why I took offense, instead of just laughing at his foolishness.