So, what do you do when you're a big star with a big, bulging wallet and a big pack of paps following you all over town? Think small.
Squeeze into the tiniest car you can manage, as Liz Hurley did last week when she went shopping in London. The sunglasses were big, the hair was big, but the Fiat 500 she was driving was smaller even than her chances of making a decent movie ever again. It does 50 miles to the gallon and has low CO2 emissions.
Ms Hurley has not previously shown herself to worry about such things: she flew her wedding guests list to India, which was not so much a carbon footprint as a great big boot in the face of the planet. So why drive a piccolino Cinquecento?
Better ask Wayne Rooney, the biggest star in the England team, who chose to leave his Land Rover and his Lamborghini behind and drive to Manchester United's training ground in a Mini on Wednesday. A special £25,000 GP version, obviously, with alloy wheels and sports suspension, but still a Mini. He has always been a fan, having bought one at the age of 17, before he could drive (Wazza failed the theory test twice).
Voted the Car of the Century in 1999, the Mini was driven by Britt Ekland, John Lennon and Steve McQueen during the Sixties – Marc Bolan died in one in the Seventies, but let's pass that one by more effectively than he did the tree – and present-day fans of the relaunched version include Madonna and Jeremy Clarkson. "By any rational standards this is a terrible car with a boring engine and no space in the back," says the Top Gear presenter. "But the signals it sends out are that you're not wearing any knickers."
Nor carrying much luggage. Still, you can get more in a Mini than you can in the tiny electric G-Wiz, beloved of Kristin Scott Thomas and others.
But Mr Clarkson has missed the main signal sent out by a star in an unreasonably small car. As a tall man who once owned a Smart, I know what that is. There is fun to be had in waiting by the lights with a growling Ferrari, then nipping into a poky parking space while the supercar overheats. You can get a cheap laugh out of passing a boy racer on the motorway at 84mph (the Smart top speed, which feels like twice that in a car so light). But you do have to be able to take other people laughing at what looks like a living cartoon of a massive geezer squashed into a dodgem. What the stars are saying is that they don't care what anyone thinks. They have so much money, they can afford not to.
For Wayne Rooney to drive a Mini is a way of saying he could afford any flash car in the world. You need the nerve to carry that off, though. Size matters. So the one thing you can say about a star in a small car is that they have a really big ... ego.