Rebecca Tyrrel: It isn't every Jewish grandmother who'll re-enact torture scenes from Abu Ghraib for her grandson

Who knew that Joan Rivers was waterboarded by her own grandson? And who knows why 10-year-old Cooper chose to style himself as the Dick Cheney of the fourth grade?

Perhaps the boy was responding to the Rivers gag that goes, "The only child I ever liked was Helen Keller, because she couldn't speak" (a rib-buster for which she was heckled by a man with a deaf and dumb child). Had the boy heard the entire act, he would have understood the futility of using torture to extract information on this particular victim. With Rivers, as much now at 78 as for the last half century, the tricky bit is stopping her confessing the most intimate details of her life. "The only way I can ever hear heavy breathing from my husband's side of the bed is when he's having an asthma attack," she said before poor Edgar committed suicide in 1987. Together they begat Melissa, Joan's co-star in the TV show in which Joan moves in with her daughter and grandson with every apparent intent of ruining their lives.

It was on this festival of mirth that little Cooper and his gang of chums laid Joan out on a makeshift gurney of leaves and twigs, and poured water on to her face from a watering can. Not of course that she, after so much Bride of Wildenstein plastic surgery, will have felt a thing. She used to look her age but these days she doesn't even look her species is what they say about her. And what with the children's poor aim ensuring that little of the water entered her lungs, after histrionically gasping for air and clutching at her bad back, she was able to describe Cooper and his friends as "the cutest little infidels I have ever seen".

It isn't every near-octogenarian Jewish grandmother who will indulge her grandson by re-enacting scenes from Abu Ghraib for his amusement. So small wonder that Cooper "absolutely adores her", according to Melissa, "and he does call her Grandma, even though she wanted him to call her Nana Newface".

As for Joan herself, she says, "I am so bored they are giving up torture in the United States. Oh, waterboarding, waterboarding, big fucking deal. Try getting a Brazilian wax and you will give up secrets you never thought you had."