If it feels safe, simply asking someone why they are bullying can sometimes be a surprisingly effective way to get them to stop.
Only when and if it feels safe, ask someone why they’re bullying someone else. A question like, “Hey, why are you bothering her?” forces the person to explain themselves and can get them to stop.
The next time your friend makes an offhand remark about women, question it and point out that offhand offensive remarks aren’t harmless--studies show men who hear sexist jokes are more likely to tolerate sexism, and are more willing to discriminate against women.
When questioning someone’s behavior, consider phrases like, “Why are you doing this?” or “Do you really like being mean to people?”