The action of flashing whilst on Splash Mountain, or indeed any log ride, at the part with the cameras. However since the 70's they won't allow the photo to be shown on the screens but if you tell the photo person beforehand there's a good chance of you getting the ultimate show and tell of DisneyWorld!
Dude 1: When we went to DisneyWorld Shannie got so drunk we convinced her to do a Flash Mountain!
Dude 2: That's sweet, you get a photo?
Dude 1: nah man, the photo dude didn't screen it and everyone saw her boobs. They're getting that bloke fired and she's now banned, its on the internet though!