I need to channel my inner Jerry Springer

So I'm walking down a fairly busy street near my house on my way to pick up the Boy from daycare. It's a bit chillier than I thought and I'm wondering if I dressed the Little Guy warmly enough. He's sitting in the stroller thumping his legs and jawing away to himself as per usual.

Halfway down the street, I come upon a bunch of teenagers hanging out. There's about ten of them in a clump, and they're blocking the entire sidewalk. They don't see me or the stroller (naturally), so I stop and politely say "Excuse me" audibly enough to be heard over the giggles and guffaws. They reluctantly make a path in the knot of bodies just large enough for me to pass. I walk through, and just as I'm a few steps beyond the group, a blond girl speaks up, her voice nonchalantly oozing disdain:

"Your baby is fat."

I look back, not sure I heard her correctly. And then she laughs. And not in an 'I just made a joke' way. I heard correctly. I shoot her a look so dark, I'm surprised she is still standing upright. I hold the look but she looks away, dismissing me. I want to do something but I'm in a state of shock. Who insults a baby? In front of the baby's mother?? I am livid. I want to go back and say:

"The Little Guy may be on the larger end of the spectrum, but he's a baby. He will lose the baby fat as he grows. Your lack of civility, however, is a much more difficult problem to address. You are lucky that I am in shock from your appalling lack of manners, or you might find yourself in a conflict you have no hope of resolving."

Or, as they would say on Jerry Springer:

"Yo skank! Yeah you, with the puffy jacket and the painted on jeans. The baby may be large, but you're a b*tch. He, at least, will lose the baby fat. You'd better duck before I throw my shoe at your head."

Don't mess with the Mama Bear. The claws will come out.