Who's side do you take?
Does it matter if the other person is close friend or relative vs someone you don't know as well?
I get the impression many people have the mentality that you always have to take your SO's side. On the contrary, I feel the correct side to take in any argument in is always whoever you believe is right, regardless of who is involved. It should of course be explained politely, especially if one of the people is your SO or someone else close to you. When I turn to someone to settle a debate I seek a nearby person who I think is knowledgeable at the subject, not the nearest person I think will agree with my side.