Originally Posted by ClipperClub
Im not sure why other posters have implicated other aircraft, as the engine exhaust closest to the OP would be their own aircraft!
The air for the cabin comes from the engine intakes. The engine's exhaust is on the other end of the engine and comes out at a high velocity and doesn't normally recirculate back to the engine intake. If it did, the engine wouldn't operate normally so the engine is designed to avoid that situation. It is possibly on the ground, however, if you have a pretty strong tailwind blowing at just the wrong angle but this does not happen very often.
When on taxi before takeoff, the cabin is not in a fully compressed state so air travels freely between inside/outside through the door seals.
That's not how it works.
Turn on the A/C in your car and crack open a window. Air will go out the crack, not in, even though your car is not in a "fully compressed state". If the "packs" are on, and you don't have any doors open, air will be exiting around the closed doors, not entering.