When you plug one nostril with your finger, and blow out of the other nostril with everything you have, sending a snot projectile out of the nose.

when you've done something so cringe you can't stop replaying it in your head and it stops you from getting on with your every day life

To blow one's nose by blocking one nostril with a finger and blowing snot from the other nostril onto the floor or ground. See Farmer Snort.

n. mass of mucuous expelled by force, either involuntarily through sneezing or by closing one nostril and exhaling nasally

When you plug/cover/pinch one nostril closed and then blow hard to make unwanted snot shoot out the other nostril. Sometimes when suffering from a cold, snot rockets can be achieved by the nose alone, without intervention from the hands. The primary purpose of the "rocket" is to avoid leaving any snot residue left behind. The idea is to blow the snot out fast enough so that it has no chance of sticking to the end of your nostril. Snot rockets are enacted primarily in situations when tissue is desperately needed but unavailable, or it is done simply for recreation.

What my boyfriend did on a date.

When a projectile booger comes shooting out of a person's nostril.