An unexpected strike; an ambush. A blow delivered when the recipient is not looking. (ex.) We were arguing over nothing when I turned and he slyrapped me.

It is a portmanteau(blend) from sly meaning sneaky or underhanded and rap meaning to hit or wallop or strike.

As for it's origins it's been in my lexicon all my life. I really can't be specific other than say it is street jargon rememberedfrom my days growing up on the streets of The Bronx, NY.
(ex.) We were arguing over something inconsequential when I turned and he slyrapped me.
by CelticNomad January 24, 2018
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