Question: How many adults standing up for their children become infantile themselves?

Answer: Well, at least four, according to God of Carnage.

Following a playground contretemps between Ferdinand's stick and Bruno's teeth, two sets of concerned parents meet in an attempt to smooth things over. In the blue corner, Alain and Annette Reille: an unflinchingly cynical lawyer, and his wealth manager' wife. In the red corner, Michel and Véronique Vallon: a wealthy tradesman and a bleeding-heart writer with a penchant for oppressed Africans.

The professionally abrupt vs. the phoney trendy . . . Well, you can see where this is going. Alain (a haughty, quick-draw Ralph Fiennes) is already sour about a point of vocab. Was his son holding' this stick, or wielding' it, or brandishing' it? He wants to know what's being implied. For her part, Véronique (Janet If you can't book Cate Blanchett' McTeer) can't see why Ferdinand doesn't just drop by and apologise. "Madame," snorts Alain, "our son is a savage."

The graceful Annette (Tamsin Greig) and the gruff Michel (Ken Stott) do their best to keep things peaceful; but it's not long before sweet-mannered talk of practising "the art of coexistence" (social code for your child is obviously an insufferable turd') descends into undisguised sarcasm.

The husbands start to relish the proxy tussle, and recommend man-to-man solutions. In retaliation, Véronique throws a five-star strop, and Annette gets smashed on Michel's top-grade rum, staggering around like a baby giraffe doped by prankster veterinary students (albeit with significantly nicer legs).

As always, Reza's genius (she, of course, the writer of Art) is in the sparking, destructive energy generated between her characters. The disagreements start small, over recipes (the cutting of apples and pears, specifically), "the pacifying effects of culture", and other such awful suburbanalities. Every conceivable clanger is dropped: tempers fray and social niceties fall by the wayside. The arguments move into more personal territory.

The punch-line nature of this build-up-and-release should tire, but it doesn't. On the contrary, the audience relished the predictability of every waspish retort and acerbic put-down, and broke into gleeful applause at every wrong line delivered in exactly the wrong way at precisely the wrong time.

d=3,3,1God of Carnage is true and it is hilarious. In fact, it's hard to imagine how it could have been any funnier. The laughter from all quarters was deep and knowing and prolonged. My brother and I sniggered about (at) our parents. The mums in front chuckled about their kids (in absentia - for shame). The geriatrics beside me wheezed openly at each other. Men and women whooped and hollered alternately, and even - it happens! - together. But everybody was laughing. Everybody.

God of Carnage is at the Gielgud Theatre, booking to June 14. For tickets call 0844 482 5130 (www.godofcarnage.com).