Nothing; walk away and leave them to it.
Shrink into the background and wait till it finishes.
Break it up and calm everybody down.
Start laughing and making jokes. It may make things worse but it`s funny!
Make yourself noticed. They know their place and stop arguing.
Call a mate over to help you sort out the problem. Two is better than one!
You wait for the right moment to say something that you know will make them calm down.
Be farely agressive towards them to get your point across.
Get hot-tempered and angry. How dare they start this argument in front of you!
Actually become insulting and agressive. Do anything to make them stop arguing.