The true white privilege is being able to do that without fear of being shot.
Having said that it is also the only appropriate way to use it. Way to go lads!
At the risk of coming across as argumentative, I'd like to point out two flaws in your first sentence.
The first is missing that the real "true white privilege" is being able to fly the flag of an enemy state and not be tossed in a cage. Imagine what would happen to some brown-skinned dude waving an ISIS flag. Of course, I acknowledge there is some privilege at play that I am able to exploit, but it is not the most important one in this scenario.
The second is assuming that I had no fear. Believe me, I had plenty. We were outnumbered and outgunned. Had that argument progressed further, who knows how poorly things could have gone for me or my friend. All it would have taken was for the cops to either not be paying attention or to be on the side of the racists. If I had wanted to truly flex my white privilege, I would have just stayed at home. I could easily sit this fight out. It's kind of like, although not exactly the same as, how a masculine gay guy can evade homophobia or how a light-skinned black person with European features could "pass" as white to get around racism. By engaging in this activity, I firmly assert my status as "race traitor" or whatever to people who take such things seriously.
These points aside, I appreciate your comment.