I'm also terrible at doing this, too. I think you're right though - it is easier to do it for someone else! But when you're in a confrontational situation that you haven't sought (unlike a salary negotiation, which you have probably sought), it's more about the "seat of your pants" type stuff, in which I tend to try to avoid escalation and/or the confrontation itself. Of course it's always easy to come up with "well I should have said x" or "I should have kicked him in the y" after it's over.