Abbreviation of Hoist By Your Own Petard.
Could also be "HBHOP" for "His Own".

Part of the Counter-Strike "culture". Used by pedantic geeks to make fun of people that do damage or kill themselves in game.
"OMG, lolers! U GOT HBYOP!"

and
more clasically....

"For tis the sport to have the enginer Hoist with his owne petar". - Shakespeare, who gives the line to Hamlet
by ElJoker September 19, 2007
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