Yes Twilight why can't you and your friends be more reasonable when it comes to addressing anyBODY, not just anyPONY? Its perhaps just a few folks like me but it rather irks me how the citizens of Equestria and ponies elsewhere choose to address a collective group as any/some/no pony, even if a sizable group of the populace addressed in question aren't in fact ponies at all, or considered as such.
So the better question I feel compelled to ask is, who does the term pony apply to and why is it applied? Is it a simple matter of Equestrian grammar and linguistics or is it an implicitly form of racial and national identity, like the terms American or British? Even the non-ponies in Equestria, say for example the Donkey Cranky, use the term applying it to themselves. In fact, someone may correct me if I'm wrong, but I haven't recalled the term Equestrian being used to refer to any group of people. Sure for events, locations and places, but not people. This might be justifiable for races species like donkeys, mules, and sentient livestock as well as accepted or assimilated characters like Spike and Zecora, but the use of the term suggests, unintentionally or not, a bias or dominance over other equally worthy beings.
Even Princess Celestia herself refers to her vassals as my little ponies, though of course a lot of the times she's addressing the Mane 6 so this might be understandable. I still regard her as probably the most rational and progressive of the characters, as in being open to everyone, considering the many subtle gestures she does for others, but the tone and implications are still there. It would be very interesting to see how Celestia interacts with non pony characters like the bison, Zecora, or even the cattle so I'll be hopeful to see her progress in this and many other dynamics in the future seasons.
Yes the show is called My Little Pony, but its also called and its main theme is Friendship is Magic regardless of whether you're a pony, brony, zebra, donkey or even a human (as seen in Equestria Girls).