I've been using this AWESOME neg recently that I came up w/ and to be honest, I'm very proud of myself.
I noticed down at the beach TONS of women wear out dresses that have loads of flowers etc. on them so I go up to them and say,
"You look like a flower girl in a wedding! haha where's the bride"
Jokingly of course, and it HAS NOT failed me yet...
If you say it in the right tone/context it'll come off as a solid neg and she'll start proving herself to you.
Give it a Field Test and report back w/ your results!