Learned this the hard way. Back when LinuxCon was still called LinuxCon, I made the mistake of making a beeline to the first "booth" I saw that was manned by a fellow female. I studied the setup, ascertained what kind of hardware being shown off by this particular vendor, and proceeded to inquire along the line of shop talk. Although I don't remember exactly what I asked her, this was the gist of our exchange. BB: "I…
My friend raised her hand - and in horror, the presenter recognised her as the woman she'd assumed was someone's partner back at the registration desk and tried to get to sign the partner's program (=daily things to do while your techy partner is doing the conference). Yes, the female anti-sexism speaker had herself assumed a female delegate was merely a hanger-on, solely because of her gender.
It's both "ha ha" funny and disturbing funny, that sexism is so ingrained that someone who should absolutely know better still fell prey to it.