do not, i repeat, DO NOT approach anyone to lecture them about their bag - because that's what you're doing, even if you think telling them about your bag's superior craftsmanship is the 'polite' option - it's NOT.
in either situation the girl would have every right to WHACK you with her big fake bag. hell, if i was within earshot, i'd probably grab my big REAL bag and whack you with it.
just like it's RUDE to 'politely' approach a woman and tell her that her breast implants make her breasts look obviously fake and you're worried about her self image, it's RUDE to tell someone that their bag is fake and they should only buy real ones for whatever reason, even if you try to do it 'politely' - the action is inherently RUDE and NOT CLASSY, and therefore cannot be done politely. it's not any of your business, no matter how sensative you are to copyright issues. there are plenty of writers, musicians, designers, artists, and craftsman out there that manage to not make an ass out of themselves in public. JOIN THEIR RANKS.
i'm sorry, i know i'm probably not being as tactful as i could be about this, but this is such and EGREGIOUS breach in ettequite that you should be embarrassed for your bad behavior - just remember, the other girl wasn't the ONLY one shouting assanine things in that bar that night - YOU WERE TOO, if you said what you said.