Lol, happened years ago - but pertinent to all sorts of situations (school, work, new boyfriend's family/friends etc). Question of etiquette, manners and you said it - age :) See it happening with young people when I go out. Hurts. Think everyone goes through it. Maybe that's why we don't do it when we're older :)
Awful when this happens. At least it helps you find out who your real friends are! The problem is with them, how immature. Next time they invite you somewhere tell them no thanks that you don't wish to go as they were so rude last time.