Karate chop. 1. The angle of the chop suggests slanted eyes, 2. Karate is stereotypically all Asians ' martial art, 3. Classifying all Asians as Japanese
Peter stepped on my shoe so I caught him with a jap slap to the head.
It means multiple things. Basically, its a WWII reference, meaning:
1. Karate chop. Japanese were known by soldiers for their superior hand to hand combat skills, particularly in karate.
2. To strike a person unexpectedly, similarly to a sucker punch.
3. Loosely, it refers to an unexpected attack or ambush.
Wow! Did you see Tom get into a fight, yesterday? He hit that guy with a vicious jap slap and almost knocked him out.