Not a bad question...

Trying to think. The longest of any girlfriend or romantic/sexual partner I've had was a thick ponytail down to her her hips. I also had a study partner once whose ends were even longer, covering almost all of her butt – but she quickly changed majors and I didn't see her much after (nor did I have the chance to pursue her) – she trimmed her hair to waist/hip-length, though.

There was one girl in uni with an absolutely MASSIVE bun, that she never ever took down; neither in school or out in the city whenever I happened to see her. No idea how long it was, hard to calculate the coils with such thickness.

There were a couple of girls with thigh-length hair that I just happened to cross on the street, or such.

Two girls I saw with knee length hair. One whose ends were tapering by that stage, and she later cut to classic-ish. The other – a romantic pursuit of mine, which never worked out, thickest haur I've ever seen – ended up cutting to tailbone, then growing it out again. Haven't seen her in quite a while.