'IF I WAS TO HIT THE BACK OF YOUR NECK WITH THE EDGE OF MY HAND....'

This was usually said to impress people and to indicate that their stint in Japan or elsewhere was not all spent in bars and nightclubs,etc. as they struck the table(s) with the edge of their hand(little finger side in a shuto) usually in bars at that, after a few drinks and questions about if they had studied karate or martial arts and they didn't want to lose face, so-to-speak,especially in front of girls.