Frequent Flyer

Upon unlocking it, pick the Sabre (the fastest plane), pick either any mission that has a border (usually survival) OR select Organized with difficult NOT set to easy.

Hold W/UP to the border, restart and repeat. Each game will last within 5 seconds, and the counter will sharply increase.

Be aware, for some reason the cursor is set to move with WASD & Arrow keys even when hidden. You'll have to readjust your mouse on each mission fail.