I agree that you shouldn't have to ask, if they are friends that can swing it they will offer. But I also agree with others that you have no beef. If you don't like it, don't ask them. Hell, they may be going because it's free, otherwise they would play a different course, with other people, or not at all. I don't know the situation here.

All of that said, I will gladly buy you beers all day long for a free round.