Green’s Dictionary of Slang

1. (UK black) to kill, to murder; as adj.: dead.

2008		A. Wheatle Dirty South 59: Something happen to Red Eyes? Has he been duppied?
2018-20		T. Thorne (ed.) ‘Drill Slang Glossary’ at Forensic Linguistic Databank 🌐 Duppykill, defeat, attack; dead.
2020		G. Krauze What They Was 20: Bunny didn’t actually duppy any of the brers who robbed his people .

2. (UK black) to rob with violence (in the street), to beat up.

2015

www.reddit.com/r/hiphopheads Grime Terminology Guide 🌐 Duppy/Duppied - Mugged/Robbed on the street/Beaten up.