When someone is in front of you and without warning you get your hand between there thighs and slap there thighs back and forth saying "Slappy Salmon"
I was behind my friend walking up a flight of stairs and it was a perfect opportunity to give him a slappy salmon. I gave him a slappy salmon and he turned around and yelled "knock it off" he was pissed.
Standing in front of your significant other, or someone else, with a big smile, swinging your junk back and forth so it slaps against your legs. Works best right after you get out of the shower.