I haven't been on this forum much lately, but I am going to share my all-time favorite neg with you guys:p
Part of my natural game so to say, but it's only something I've noticed recently....
Here it is:

Her: Are you coming on to me? Are you hitting on me? Do you think I'm cute? or whatever....basically her asking if you are showing interest.
Me: Wait....wut? NO! I'm not gay
Her: ......I'm a girl you know
Me: For real?:P*Just laugh it off and tickle her/ hit her playfully or something*

Very important note though, keep it subtle and playful. If you are plain saying she looks like your fat uncle Bob or Hulk Hogan, you are taking a chance.
She might feel attacked because what you are doing here is attacking her femininity.

I just like to keep it light and playfully, mix it up with my (from time to time) witty character;)

Let me know what you think:)

I kinda like that, but yeah like you say it must be pulled off right or it might be more of an insult.

How about instead of asking 'really?' you take a good deliberate look at her tits and say 'so you are' with a cheeky half smile..

One time a girl turned it back around on me though. Putting her chest forward and saying excuse me? Then what do you think these are?

I think I had replied something like, My god modern science can do nearly anything with those female growth hormones:o

The joke kinda broke the awkwardness, when it started getting hot and heavy;)

You know like pants down, oh so you are a woman! :p