You earn a great deal of money if you're part of the cast of a hit American comedy like Friends. But there are drawbacks, because this money flows from syndicated sales to television stations all over the world. The more substantial of these have to be kept happy about their expensive purchase. They have to be made to feel like friends, in short. Which means that every now and then you will be required to emerge from your luxuriously appointed dressing room and pretend to have fun with the syndicating station's zany of the month. For Channel Four this currently means Johnny Vaughan, whose personal brand of inverted quotation mark broadcasting (everything that isn't a joke is a quote, or rather "a quote") has given The Big Breakfast a much needed ratings boost. In The One Where Johnny Makes Friends (C4) he talked to the stars while they filmed an episode in London, a series of interviews in which the pungent odour of contractual obligation kept breaking through the atmosphere of bantering equality. Talking to Lisa Kudrow, marooned in Los Angeles by pregnancy, Johnny asked for advice on how he could best break the ice with her co- stars: "You know the best thing to do with any of the cast", she said, "leave them alone!" It was the most explicit cry for help in this often excruciating programme.

The central conceit was that Johnny was pretending to be a gauche nonentity - a joke which rather depends on feeling confident that neither word could conceivably apply to him in real life. But for the cast of Friends, subjected to this kind of conveyer-belt intimacy week after week, the distinction between an ironic prat and a genuine one is likely to be immaterial. None of them were rude exactly - though Courteney Cox came close - but you could see their eyes flicking wildly sideways now and then, as if seeking guidance from a nearby minder. "I don't get it" said Matt Le Blanc, after being given a tin of Ronseal varnish as a jokey farewell present. If any of this had peeled the veneer away - as Ruby Wax sometimes manages to do - the effect might have been a little less tiresome. As it was it delivered a most unusual blend of sycophancy and impertinence, relieved only by numerous extracts from the series itself.

There was more synthetic fun in On The Piste, a Channel Five series which extends the Brits Behaving Badly franchise pioneered by Sky's documentaries about holidaymakers in Ibiza and the West Indies. Filmed in Meribel, it concluded last night with several students from Bristol skiing naked down a slope in the early hours of the morning. It seems frankly inconceivable that any French resort would keep a lift open until 2am for the convenience of drunken oafs wearing nothing but hula skirts - so I assume this excursion was arranged with the help of the film-makers, who must have indemnified the local authorities against potential lawsuits for intimate frostbite. One wonders whether the producers also encouraged the lively snowball fight between French and British tourists which concluded with one of the combatants giving a husky dog christening to the bonnet of a nearby car. I liked the ex-military man who punctuated his pompous instruction to his son with regular prat-falls - but if bare buttocks and beer races aren't your thing I suggest you turn elsewhere.

Aviators, a BBC2 series about the early days of flight, combines maddening affectation (aeroplanes filmed as if the cameraman has been handed a Super- 8 cine camera and strapped to a Spacehopper) with wonderful inventions - as the programme described how post-war euphoria about the possibilities of flight turned more fearful the screen showed a montage of old photographs of people looking skywards, a sequence which exactly caught the ambiguous feelings aircraft can still sometimes evoke - a mixture of dread and wonder. It was sobering to realise that astronauts now occupy the mythic space once held by airmen - perhaps they too will change from exemplars of global cooperation into a novel kind of terror.