Thump. Thud, thud. Whack! Whack! Whack!

You’re halfway through your entrée when the child in the next booth goes all Keith Moon on your backrest.

First you ignore it. When the pounding continues, you glance over at the parents — the universal signal for, “Your child needs guidance, or restraints, and I don’t care which.”

His final blow sends petite sirah sloshing down your dry-clean-only date-night blouse, and you launch over the booth, locking eyes with Thumper.

“Sweetie,” you say between clenched teeth, “there’s a person sitting here. It’s time to stop.” Considering what you were really thinking, the comment is friendly, sensitive, and generous. It doesn’t matter, though; you could say, “Thank you, sir. May I have another?” and it would still cause the drummer boy’s parents to regard you as though you’d just stabbed their musical angel with your salad fork.

My mom friends say they feel “hateful” and even “violent” when someone else — particularly a stranger — reprimands their kids. And I honestly don’t get it.

My grandmother and aunt were preschool teachers who felt not only comfortable but obligated to correct strangers’ children when they were misbehaving at the grocery store (“Please sit down in that cart, sir”) or movie theater (“This is the part where you stop talking and listen”). I don’t mean yelling at them, or grabbing them. I mean correcting them when they’re doing something dangerous, destructive, or disrespectful. Which they do frequently. Because they’re kids.

There are a few situations in which most moms agree it’s fair to call out someone else’s kid: If there’s a risk of physical harm, if it’s at your house (your rules rule), or if it’s a close friend or family member where “hey, cut that out” privileges are well established.

Otherwise, etiquette experts say admonishing someone else’s monster is bad form. Especially if his mom or dad is right there.

“It is never okay to reprimand someone else’s child when the parent is present,” says manners coach Constance Hoffman of LearnSocialGraces.com. “We like to think we have it all figured out and know what’s best for our little darlings. By offering unsolicited advice, you risk offending the other party.”

Unless the other party is me. I hail from the it-takes-a-village village. As long as the criticism is fair, I’m grateful when someone calls out my kids on their stuff. They learn that the whole world is affected by their behavior and will hold them accountable for their actions.

But this approach falls apart when parents disagree on what’s reasonable behavior. If I expect your daughter to be polite at a kid-friendly restaurant — and you believe kid-friendly restaurants exist so that your daughter doesn’t have to be polite — then you’re liable to get huffy when I ask her to stop flicking french fries at my head.

“The trick is to reprimand kids without making the parents feel like they are the ones being reprimanded,” says parenting coach Judy Osterhage of FamilyFuel.com. “Say, ‘Hey, let me help you down from there. I want to make sure you’re safe,’ instead of, ‘For chrissake, woman, get your child off my counter.'”

Maybe it’s pointless; maybe critiquing other kids’ conduct is a futile exercise undertaken by insensitive control freaks (hi, nice to meetcha). Or maybe it’s the most noble cause on Earth.

“The purpose of your comments to someone else’s child cannot be to parent that child, or to fiddle around with his eventual character,” says child psychiatrist Elizabeth Berger, author of Raising Kids with Character. “The purpose of your comments is to communicate in the here-and-now; human beings communicate with one another, with dignity and honesty and clarity, about matters of mutual concern.”

And if that doesn’t work, we start flicking those fries right back.