originating from jamaican folklore, it is slang for a ghost or spirit, but nowadays is used as slang to hit someone or beat someone up, or take them for a complete derkhead. duppy is degenerately used by black people who are looking for a fight or little white kids who want to or think that they are the black gangsters....eg
"ill duppy you sam"
"i will take you for a complete derkhead fool"
Watch me duppy this waste guy
observe my beating of this idiotic male