What do you think girls think and say of boys? This is just stupid (and incorrect) victimism, directed at a gender, when the other one acts the same.
Someone using that argument is either 1) completely unaware of the experiences of the other gender or 2) being dishonest.
There's definitely still a strong 'boyish' culture where boys can say almost anything they like and it's OK, but girls (for whatever reason) won't. It's not about who's better - it's about what we let people get away with.
Also it's not about thinking. Thinking is the ultimate change you want, but we can't see and know what people around us think, but we can still try to enact standards of reasonable, gentle (non-violent if you will) communication.
I have very rarely encountered any hostility towards women in professional environment though.
I you hear that a lot in your environemnt - maybe its time to speak up against it and/or change it for something better.
School was much more set up for girls and they were more successful on average.
I don't remember boys saying girls are dumb or the reverse. The stereotype was more about girls being obedient and tidy and organized and serious while boys are messy, forgetful, chaotic and mischievous.
Edit: this last point also makes it weird for me when people equate male with order and female with chaos. I guess the stereotype may have reversed since then? Or the adult stereotype is the reverse of the child stereotype?