A
Underwear is also pretty sexist. As are different trianing regimines at the gym for women vs. men. And nutritional requirements for women vs. men. Different recommendations for sungliht exposure for Irish vs. Nigerians is racist.
Yes, and no. Beware of committing the logical fallacy of Equivocation - switching the meaning of a word mid-stream.
Sexism has two definitions: 1) Prejudice or discrimination between sexes and 2) placing a value judgement on one sex or the other.
Now, with underwear, one may "discriminate" (technically meaning "differentiate") between the sexes because the bodies are demonstrably physically different - the clothing may need to be cut differently to fit. Most men simply don't need brassier, but many women do for their comfort. There is no judgement of value attached to this.
However, if most of the underwear for sale for women is designed for sex appeal rather than comfort, and the men's stuff is designed purely for function, there are value judgements being implied.
You really need to understand that just because something is an *ism or *ist doesn't necessarily mean it's bad.
This is where the equivocation steps in. You're sticking to outmoded language use. In current use, the -ism really is about the bad forms of differentiation. Don't expect others to stick by your use, when it isn't the common one at this time. Sorry, but you don't get to swap the meaning out from under them, just because it is one you can technically get from a dictionary.