Letting people get away with sexism

In the last few months I have stewed over a few occasions where I have not called someone out on their sexism/racism/classism. Usually I am very quick to point out to people that what they've said is not okay. I imagine that I have a bit of a rep for being mean and a spoilsport and anal about things that are supposedly meant as jokes. But my justification (do I need one?) is that this is my activism because I don't get to do marching and letter writing and all that.

Most of the time I can't believe someone of my acquaintance would say what they have. I am all over Facebook people calling hacking "raping". Wrong.

But sometimes I don't tell someone they've said something bad. One was my future father in law (yeah, D and I got engaged! More on that later) so I felt rude pointing it out.

Another was a professor in my dept who had been asked to speak at a social for PhD students. He spoke about his life history in academia. His speech was peppered with outdated wisecracks about sexy female students - I can't bring myself to talk about it. I don't think he knew his audience. It was like he was still in the 1970s. And if he felt it acceptable to speak in such a way in a mixed, young audience, what does he talk like among his peers? Shudder. What was worst was that, as a professor, I felt unable to boo, hiss, whatever. I've never met him before. Everyone else clapped. Then the women I was sat with all turned to each other and we said, did he really just say that? We were stunned into silence. The social organisers had let him get away with. The other (also male) professors had let him get away with it - although they came over to us afterwards and apologised on his behalf! It has got round the department now, among people who weren't at the social. Two weeks later I am still annoyed that I let him get away with it - but I wasn't sure what I could have done. Certainly it explained a few things about my department if that is the culture that is allowed.

So, should I feel bad for calling people out, or for not calling people out? With whom is it acceptable to turn a blind eye? Those we respect? Older people who we *should* respect? If I stand my ground how do I come across to people?