Just by remaining (as much as possible) cool you've done a lot to milden the negative comment. Like you just don't care, that was DHV that you stand above things. This is how I would have reacted:
HB: You're just a little boy. This guy here, he's a real man!
Me: Haha, how you wanna tell? You don't even know me really yet. (if she really doesn't)
or an imense neg is she does know me:
Me: And what makes me a little boy? I have to see yet something from you that qualifies you as grown woman. You seem totally childish to me by making such a comparison.
or
Me: Why are you telling me this? Are you interested in me and playing the "hard to get"?
I think the last one's best as you are turning the game around.
Oh, and don't make fun of ages! I once negged a girl on her age. She was 20 and I asked her if she was 37. She pushed me out of "anger" which is good, because it's kino, so I repeated the game by saying "Yeah, you totally look like 37" a little bit later. She pushed me again and I replied "Haha, you enjoy touching me, don't you?" This time she was really angry. This wasn't just C&B, I destroyed that set.
IMO she was just trying to game you, to make you qualify yourself for her. Don't let it happen, turn the game around. Freeze her out, ignore her, befriend that "real man" and her ex and show her how she's the only one you don't like there.
And that slapping pretty much shows her intention to make you qualify yourself. She is "punishing" you for not doing what she wants you to do. Even if you don't think it was, this was a good played set considering the circumstances, since you remained as cool as possible. She slapped you, because you didn't try to qualify yourself and this is good.
Concerning the other post, you are negging too much. I once did that, too, and it turned that the girls later said I would be a total asshole, lol! I learned how hard it is to resist to repeat a neg especially if it's a damn funny one, but I noticed that repeating negs is very bad.
I think you should have given her a neutral gift like a cheap perfume, but that's just me. Show her coldness and disinterest so she has to work for your attention. A good situation would have been if you could have befriended her best girlfriend and give her all of your attention. Jealousy works wonders. She would have started to wonder "Wait a minute... He was so interested in me... Why is he talking to my friend instead of me???"
That could have worked with the two cockblocks instead of her friend, too, just like I said before.
Oh BTW, don't be nervous that you might fuck up. Always tell yourself this: "There are numerous other girls I can game, she's nothing special. If I fuck up, I'll be better off the next time when I sarge a HB9.5 who is hotter than she is and then I will have a HB9.5 instead of HB9. HECK! GOOD THAT I FUCKED UP HB9! That way I made my way to HB9.5.
"