This clearly doesn't happen to you then.
Believe me mate, you are incredibly naive if you think the type of person that does these things does them only once. The mates that I am talking about are notorious for it. The reason they get themselves into trouble in the first place is because they think I will get them out of it. As soon as we are all out together they, one in particular, struts around like the cock of the walk because they are out with myself and my other mate (both pretty big). In the past we have bailed him out simply by going over and talking to people, they often calm down when they realise they are dealing with 2 6'5 18 stone guys rather than the 10 stone mate of ours. We got fed up of them getting into trouble and running to us expecting us to deal with it so eventually we just left him to it. He soon stopped it in our company, although my guess is he still acts like an idiot when out with other people. When he did get a slap we simply explained that it was either that guy that was going to hit him, or us that was going to.
Don't get me wrong, I would never let any of my friends get a pasting if I could help it. As soon as enough is enough I'll try to stop the fight, if I end up involved then at that point I will stand by my friend but when someone deserves a slap they deserve a slap regardless of whether they are your friend or not.
Thankfully most of those days are behind me as I'm getting on a bit
Oh.... to the op... tell your mate not to jump in front of my car again