I've [only] been to three tech conferences. The only "sexism" I observed was excessive delight: "Oh wow, a woman!" which I hardly consider harassing. No one meant disrespect; rather the opposite. Possibly offensive is the notion that it would be a surprise to find me there at all. I might say something similar to a man at a needlepoint conference. Yes, I got sexual attention, but only in a social context, and nothing…
> The only "sexism" I observed was excessive delight: "Oh wow, a woman!" which I hardly consider harassing. FWIW some people would consider that unwelcoming/harassing--I think the term is "othering". i.e. what's treated as important is not the person or their skill but their gender. And, yes, it can be annoying for guy in a "traditionally female" domain as well.
I think sometimes in an attempt to be enthusiastic about women attending events, it can go a bit too far. Tokenism and othering as, in the long term, just as damaging to gender relations.