The automatic response usually anticipated to avoid an unexpected act they may cause you Insult or injury.
It is an reflexive action.

When you eat dirt for the first time and leave your family to build a shack in the woods

1. When some one is about to hit you and you do that sudden movement = a flinch

2. Totally cool, Flinchen

And involuntary movement made when someone is about to hit you/you think someone is about to hit you.

Replaces the word "nub", "noob", "nubstick". Refers to a particular GT on the XBOX live network. May also refer to having freakishly large thumbs. Most often used in relation to the Battlefield 3 game on Xbox.

When u hit some one on the back of the neck when they flinch

to flinch the competition : verb - To con more people into buying waterbeds than anyone else