How do I say "negging" in Chinese?
'Negging' is a specifically coined term by the author of a specific book about methods of picking up girls. I presume the end game is either acquiring a life partner or building a casual romantic relationship with a woman.

Negging is in effect, a code name for a technique, and this technique is using subtle and mild insult to manipulate the target to 1. be curious 2.feels challenged 3. be willing to engage. 

The true goal is not to repel but attract her. It is opposite of another  technique pozzing: (whereby one pays a person a compliment in order to gain their affection)

Since it is not a general English term, I think I would treat the translation with more liberty

There's an idiom in Chinese called: 欲擒故縱 (When you try to capture a target, intentionally distance yourself instead of approach closely)

If pozzing (奉丞手法) shows a 欲擒態度, then negging (挑衅手法) would show a 故縱態度 (displaying dismissive sign to attract the girl's attention and get her to engage) 

I would translate "to neg" as "挑衅" and "negging" as "挑衅手法"