Me: Here's a bug.

Male peer: I don't know why that happens. Not my fault.

Me: One way that can happen is if you do X.

Him: (condescendingly) Of course you could do that, but I didn't.

(Ok then! Done teaching.)

Separately, other male peer: One way that can happen is if you do X.

First male peer: Oh, you're right.

Again. In 2021.

I didn't say he did X; I'm not in his head and wasn't looking over his shoulder, so how would I know? I just offered one (common) way that this particular problem manifests, because we've seen it before. But from me it wasn't worthy of consideration.

This sort of thing happens far too often, even now, even among people who in other regards present as open-minded and inclusive.