first of all, slapping him in an RNC was a silly idea...
weight up the pros and cons - basically the only pro was to "teach him a lesson". apart from that you had that age old peer pressure from the other males, and the will to do what makes you appear to be a big tough man.
you had the good sense to walk out, now have the security in yourself to get over the macho bullshit.
if he had attacked you it would have been different.