Starbucks has made a simple request: do not enter one of their establishments while armed. That's a fair request, but it's not that easy to enforce. What will Starbucks do in the event that someone fully aware of this request chooses to enter with a firearm anyway?
They'll continue to serve them, because not only do they want their business, they don't want to piss off someone that's carrying a weapon.
This is what CEO Howard Schultz told the New York Times. "We are going to serve them as we would serve anyone else." In an open letter, he explained the obvious danger that confronting an armed individual presents. "Enforcing a ban would potentially require our partners to confront armed customers, and that is not a role I am comfortable asking Starbucks partners to take on."
Don't bring your gun into a Starbucks. If you do, they'll still serve you your Mocha Frappucino