Stuff white people like...

. . . and what's this getting offended on behalf of other people? . . . . If i hear someone called a Paki it's offensive to me; because it's inherently cruel and unjust, because it makes life less pleasant for all of us. I'm not offended* on behalf* of that person.

I think what is meant by 'getting offended on behalf of other people' is when these other people are not actually offended at all - the vicarious taking of offence on behalf of others might have some resonance if it accurately reflected the offence taken by the people being targeted - sometimes it doesn't.