LOL my best friend did that
Infront of our school is a giant puddle, which noone has ever seen the bottom of, cuz its been filled with water for as long as i can remember, anyways, she was driving back to school from lunch (in a early 90´s cavalier) and her friend sed *JUMP THE PUDDLE!* so she goes flying thru it, this puddle is about 20 long and about 10 ft wide. A HUGE spray of water/mud goes up, and there is the cavalier, up to the dash board in water!!!! so some guy comes over in his 4x4 w/dualies :-D (6x6?) and haules her soggy ass out of this mud puddle, when we stood in it, it was waste deep, PLUS she prolly sunk in the mud, cuz this truck put up one hell of a fight on pavement pulling this thing out! so we sat there during 5th and 6th period scooping water out of this thing and wringing out the mats and seats.
they went to see SGI (auto insurance) about it, they couldnt look at it for 2 weeks, so by the time they DID look at it, the water inside the engine started to mold and totallyed fucked up the car!!
moral of the story, if you friends says jump off a bridge, make sure you know how deep the water is ;-)