the worst ive had is blowing off chunks of clear coat , but thats always been on a beater with clear coat damage or a terrible paint job(NOT on a customers car)
used carefully at a distance you shouldnt have any issues..if the paint is flakey anyway then theres a good chance it will come off, but thats obvious !
ive also seen folk drop the nozzle on the hood...they're fighting against the pressure then when they release the trigger they drop it ...but again, be sensible and you'l be fine