GAP doesn't stand for Gay and Proud. That's an urban legend. Plus, even if it did what's wrong with it?
I know that. But the OP asked what was considered uncool and I told her. I never said the acronym but stated that other kids will notice and say it.
Note that I said I do stop the kids from saying it but they still do.
I've had to explain to some well meaning parents that have bought the once cool GAP clothes and have the kids ridiculed. If it prevents any kid from being ostracized, I'm all for it.