From the Malay phrase "penampar Jepun" to describe harsh treatment by Japanese soldiers during the Malaysian occupation of WWII.
2. (noun)A painful slap across one's face.
Don't make me japslap you!
Did you see how hard that dude japslapped him?
I'm about to japslap that bitch!
Most effective with a left handed batting style, the jap-slap has become popular with Hispanic and American Major Leaguers such as Juan Pierre and Brett Gardner.