What is the matter with my friend?

This has happened in the case of quite a few of my male friends with whom I do (or, in some cases, did) correspond with via e-mail (knew them personally). Anyway, the latest thing that is going on with the current friend is that he all of a sudden is sending rude and sarcastic emails, mostly bashing women. This is not like him. I thought he was going through some depression or something. I told him that as his cousin and his friend that I was there if he needed to talk, and he responded, "Why would you ask that?????" and when I asked him if he was OK, he said "oh yes". I had a male friend two years ago act the very same way; same thing with when I was in college over 20 years ago. Why do men do that? It's like they change overnight to someone I don't know. I'm talking platonic friends here.