Here's instructions for making a simple egg-gun. Cut the end off a caulking tube, stick a propane BBQ lighter up one end of it, let some gas build up behind the egg, then squeeze the trigger. The soft-boiled egg is propelled at high speed out of the tube, along with a satisfying jet of flame.
That is, if the thing doesn't explode in your hand, blinding you and taking three fingers off.
(Thanks, Sophia!)