Maybe a few GT kids -- if you're referring to younger kids who are newer to the program--are feeling set apart and different and defensive. So they try to prop themselves up by telling other kids, "Yeah, I'm different, what's it to you?" and so on. Not good, and it should be nipped, but can you see how it might come from insecurity and not from plain snobbery to which you're attributing it? I would wager that older kids who have been in GT several years aren't going to bother to say such silly things because they're more comfortable with being in the program--and they probably have friends across all classes.
The teachers and administration should call out any kid who mocks another kid for not being in GT -- or any general ed student who makes fun of a kid for being in GT, for that matter. But it does not help if parents buy into the idea that there is some single, universal attitude among "these kids" as if every single GT student said and thinks these same things, all the time.
How to deal with the attitude you feel you see? Get involved and be constructive, active and positive, about your school as a whole. When you're volunteering, don't tolerate gossip about who badgered the administration to let their kids in; that boat has already sailed and school's in session, so it's not relevant now to anyone but the families involved. Don't engage in discussions about those awful GT kids, or how the program is divisive. It isn't going to go away so why spend the energy on discussing it over and over? Instead, be the parent who organizes events that bring everyone together. There surely are all-school events that do not separate GT from general ed; why not work with those, and come up with ideas for more of them?
Are your GT and general ed kids in the same "specials" together? If not--they should be. In most AAP (advanced academic program, the name for GT in our area) schools, the AAP students are in orchestra, band, gym, chorus and other specials and extracurriculars with each other. In our school, kids mixed a lot in specials and on the playground, and by sixth grade, the entire class, both general ed and AAP, were doing major things as a single group including a sixth grade play that took from Sept. to Feb., and a huge camping trip that mixed the entire class in every aspect of four days' activities. Many kids in both AAP and general ed got to know each other well and made friendships outside their classes. So....if the school, the teachers and the parent volunteers work at it, there can be plenty of cameraderie. Sure, there will be some individual kids and parents with a superior attitude, but it doesn't take GT for that to happen. There does not have to be an us-versus-them mentality unless people, especially parents, let it happen through negative gossip, rather than acting constructively on behalf of ALL the kids.
Is this program a new one, or very recently established? I wonder if the administration is so focused on its new GT program, if that's the case, that it's not aware of resentments from general ed students' parents and is not thinking about building relationships across all classes. That is where parents can step in and help, but only if the parents themselves are out to build up the school as a whole.