I'm generally against the use of "prepared" lines, but I'm bad at coming up with suitable and subtle-enough negs in the field.

I've heard of "her nose wiggles when she talks! etc." (true about just about everyone)
and "phew she's really demanding/pushy; is she always like this?" (if the flirtatious intent doesn't come across properly, it can get you into hot water)

A neg is a subtle put-down with flirtatious and lighthearted intent.