An asteroid strikes Earth. I’m skydiving. Do I die? Let’s say I’m skydiving at a high altitude and, while falling, an asteroid strikes Earth. Is there a certain mass / momentum of the asteroid below which I would have a chance of surviving? Or would any reasonably sized body smashing into Earth have an impact strong enough to create vibrations through air that would kill me, or something to that effect?
Edit: I’m not certain on how big an object should be to be considered an asteroid. Let’s say it’s wider than 500 meters.
 A: The question is badly posed: survival depends not just on the asteroid mass and velocity, but also distance. If you are far away most effects attenuate a lot - the skydiving has only minor effects. 
The danger from asteroid impacts come from several sources: heat emissions, the overpressure wave, ejecta, and long-term effects. The fact that you are up in the air protects you from seismic effects (falling buildings and tsunamis). Collins, Melosh and Marcus have an excellent paper describing their estimates of the effect sizes which is used in this web app for simulating impact effects. In general the formulas are not very neat.
A big meteor impact releases heat not unlike a nuclear fireball. If you are too close you will be burned. If we assume a 500 m rock asteroid moving at 17 km/s and impacting at 45 degrees hitting 70 km away, you will get third degree burns over much of your body (but your clothing or parachute will not ignite) - since you are skydiving there will also not be any blocking objects and there is less protection from the curvature of the Earth. The overpressure is 45 kPa, which means fatal lung damage is possible but not guaranteed. On the positive side, at this distance the ejecta will mostly be fine dust rather than rocks. A 500 meter impactor also is too small to cause global agricultural failure, so it is not a civilization-killer. Just bad news even up in the air. 
One can work out inverses of the equations in the paper to get a "deadly radius" depending on mass and velocity, but it would be a rather sketchy estimate.
