I'm going to side with someone who talked behind my friend's back.
Why take a rude person's side?
I'm the only one who knows that he talked behind my friends back.
I just don't see why you wouldn't try to stick up for your friend. Friends are supposed to have each other's backs. If you let down your friend like this, they will be very hurt and may not want to even talk to you anymore.
Look, I know the other guy was rude but I need to go with the rude person on this one.
What could the rude person say that could cause you to side with them over your friend? Even if you feel they're right, you should realize that there's a chance this person will also talk about you behind your back. Maybe tell this person to not talk about someone behind their backs, and instead have a conversation with the person they have a problem with.