Cessna 150/152 Aerobats have jettisonable doors in order that you can parachute from them in an emergency, presumably after you've overstressed the thing to the point of structural failure whilst getting overexcited doing aeros.
The C172 doors have a rotating latch mechanism which positively secures the doors closed in flight- no chance of them popping open by accident. There is no jettison system.
I've had one or two nervous passengers/students on trial flying lessons and the like go into such an utter irrational blind panic once airborne that they'd do virtually anything not to be in the aircraft anymore, although stepping outside would seem a fairly daft thing to do...
As a suicide method it's a bloody sight more considerate than the uncaring b@$tard who stepped in front of a train I was on a few years ago and delayed it for an hour whilst they hosed it clean afterwards.
ST.