We all remember that Ty Lee has six identical sisters and joined the circus so she wouldn't be part of a matched set forever, but I don't think I've ever seen anyone talk about one specific sentence in that moment (I certainly hadn't thought about it before today)
And then I realized.
It's well-established that Lee is the most common, generic name anyone can have in the Avatar Universe. The perfect no-effort name to dump on a child you weren't expecting to have because no one expects to birth 7 babies in one go.
6 though? That's a sensible number. The rest of 'em can have more meaningful given names.
Thus, Ty Lee had the double burden of being part of a matched set and being the singled-out runt of said set.
That's why "Circus Freak" is a compliment. Not because she preferred the circus, but because it's a more creative name.