We hear "Is she a teacup?" practically every time we set foot outside.
I usually summarize with, "There's really no such thing, and I wish she was bigger for her health's sake." That typically leaves them with nothing to say.
Other comments: "I HATE it when people put clothes on dogs!", "Is that a cat/rat or a dog?" Etc.
I've started going with something I think I first saw somewhere online. I loudly say,
"CAREFUL! She'll take off a leg!!" 