While I'm no expert, I would have thought it'd be really difficult to get turned on with at least a dozen folks peering at you, strong studio lights burning ya backside (!) a director yelling at you and probably having to do the same scene a dozen times.
And if they do get turned on, it's only ever going to be noticable for the blokes, and i'm sure everyone concerned has seen this problem arise (pun intended) time and time again, so its no biggy (again, pun intended)