To attempt to salvage this topic for some useful purpose:
When I think of a neg I think of just a very subtle tease, always done with a smile. Something like:
"You dropped your (whatever bit of food she just dropped)."
Groom her. Pluck a bit of fuzz or a loose hair from her shirt. Excuse for kino. Makes her look better. Whats not to love about this one. It's classic, tried and true.
Call her something cute. Usually if I haven't thought up a good nickname for them yet, I call them Miss "Lastname". They think it's cute usually and it gives you personal connection. You're the only one that calls them that. A nickname routine I sometimes do is call them "Firstname" - chan. It's a japanese diminutive honorific used for young girls. You can explain to them what it means:
"Chan (ちゃん?) is a diminutive suffix; it expresses that the speaker finds a person endearing. In general, chan is used, but is not limited to, babies, young children, grandparents and teenage girls. It may also be used towards cute animals, lovers, close friends, any youthful woman, or even between friends. It can be used for males in some circumstances, but in general this use is rather condescending or intimate. Using chan with a superior's name is considered to be condescending and rude.
Although traditionally honorifics are not applied to oneself, some young women adopt the childish affectation of referring to themselves in the third person using chan (childish because it suggests that one has not learned to distinguish between names used for self and names used by others). For example, a young woman named Kanako might call herself Kanako-chan rather than using a first person pronoun. Also, the very common female name suffix -ko (〜子) may be dropped, as in Kana-chan."
- wikipedia
Those are the three tease/negs I use most often with the most success.