Women love negs even though they'll tell you otherwise.
In short, negging is about being a cheeky cunt.
NOTE: don't read if female, might be triggering.
To pull it off, you have to be confident and witty, or at least be a good actor. You would fail miserably if you come off as an imposter.
Context matters, so negs usually work better on more confident, outgoing women.
I would not spam-neg a shy girl without her being comfortable in my presence first.
Here are some examples, obviously it's best to not follow a script to a T like in pro-wrestling. The examples are just that - examples.
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When she asks you to do something together, say: "I'll have to think about it and I'll get back to you."
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You: Being "XYZ" (e.g. her profession or something else difficult she does) must be really easy.
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Introduce the girl you're on a date with as your sister to someone, e.g. the bartender.
E.g. when ordering drinks "...and one coffee for my sister."
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When a girl you've been on dates with calls, say: "Who is it?"
She: "It's Alexandra"
You: "You'll have to be more specific, I know a lot of Alexandras".
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When she asks you how she looks, or asks you how the date went: "It could be worse.".
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When a woman complains about another woman and you don't want to hear it, ask "At least, is she hot?"
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After a girl does something good, say "I take back everything I said about you to my other girlfriend."
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You: "You are smart... for a woman."
When she gets mad, tell her: "You don't know how to take a compliment, I told you you were smart."
Then she replies: "...for a woman"
And then say, "Well you are a woman, ... right?"
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After she complains about something, say: "You are proof that everything that doesn't kill us makes us stranger. You are definitely the strangest person I've met."
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E.g. on your 3rd date, You: "I have something to tell you."
She: "What?"
You: "I forgot your name."
She probably gets mad.
You: "I was just joking, I didn't forget your name."
She: "OK, what's my name?"
You: "Can you call me? I lost my phone."
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You get the point, it's about being a cheeky cunt and having fun.
If she has the hots for you, it pretty much doesn't matter what you'll say, and if she doesn't, then you'd probably want to find a woman who does.
IMO going full send is better than playing it safe but it's all very contextual.
The context is the difference between witty and cringe.