I'm in high school. I walked over and started gaming these girls, everything was running smoothly, nearing # close. Then an old set I previously # closed approached the new set and said aloud "So do you do this to all girls?"

I paused a sec, still maintaining a smile, and said "absolutely, the more the better." I tried to brush them off and continue game. I still ran the set smooth, while the old set backed off a few feet and continued to observe me. I tried to make it look like I already knew the new set to confuse the old set.
But after the callout the vibe in me changed a bit from offense to defensive and it resulted in me using a FTC and ejecting prior to # close.

How should I handle a call out like that?

Where were you?

Exactly like you did. Or ignore the comment and open them. But you need to stay congruent and plow through with shit to say. Id prolly introduce everyone to each other (doing a little funny intro for everyone IE this one is good, this one is bad, this one is funny), then use another opener then transition again.

IE:

Them : So do you do this to every girl?
You: Absolutely, the more the better.
(if they say something ignore if not continue)
You: So we were talking about... what do you think?

than transition with a cold read, a remark, a tease or just throw another attraction routine. Then isolate/qualify + number close.