Women taught us is an excuse for sexism in which the perpetrator is thought not to be at fault because women should have taught (usually) him to not be sexist.
A common version of this is arguing that mothers of sexist people brought them up wrong (without questioning the essentialism of assuming that mothers do the vast bulk of socialisation). Another is saying that of course the person is sexist, when women have not offered that person a relationship and thus the social control and education that a relationship with women is supposed to give.
A final complication is the fact that some people take an isolated incident of teaching by a woman and generalise it. For instance, when told that something they said or did was sexist, they might say "But my mother taught me that way" or "My girlfriend always says she prefers it when I do that." This can be a source of honest confusion, or a disingenuous way to offload blame for sexism onto women who aren't present.