First, I am glad that you agree that it needs to be addressed. If you disagree with everything else I think, we can at least agree on that.
I think your argument is that this is bullying, not sexism. I don't think bullying supercedes sexism. I think bullying comes in a variety of types. I don't really care if it's sexism or bullying, except in so much as it may make it easier to stop this sort of BS.
In my mind, You are teaching them to program, hence you are making them into programmers.
When I learned to drive, I learned both the mechanics of the car, but also the rules and expectations. Like let people merge, and wave a thank you to people who let you merge.
That said, there may be a better way to address the issue then trying to inculcate egalitarian values as part of being a good programmer. I didn't dig through journals to look at studies of bullying/sexism interventions in american secondary education. Feel free to do so.