Originally a word used in the ghetto of Switzerland, but brought to the US by some emigrants.
Schnäbi is the most appropriate word to identify a little (for some different oriented men: cute) penis.
It can also be used as an insult.
When someone goes to pound their fist against yours, you move to the side and make a peace sign, and if you look at both hands together, you've made a SCHNAIL! You must yell "SCHNAIL!" when this occurs.
Yours is the head of the snail and the other person is the shell. Therefore: snail + shell = SCHNAIL!