Opening an exit door in mid-flight

[Rick]

[QUOTE=JRDelirious]
Right, it doesn’t open, but someone futzing about with the mechanisms while in flight can damage something that may cause trouble later on, e.g. render the door inoperable or damage the emergency chute.
[/QUOTE]

I doubt it, and alanak’s link tends to back that up (along with a the DB Cooper answer)

For good measure, cabin doors are held secure by a series of electrical or mechanical latches, or both. So, while I wouldn’t recommend it unless you enjoy being pummeled and placed in a chokehold by panicked passengers who don’t know better, a person could conceivably sit there all day tugging on a door handle to his or her heart’s content. The door is not going to open – though you might get a red light flashing in the cockpit, causing the captain to spill his Diet Coke.

(If you’re wondering about the infamous D.B. Cooper, he ordered the crew to depressurize the cabin, then parachuted out the rear tail-cone exit, which on the old Boeing 727 did not include an in-flight lock.)