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1.
To be the target of a judge's pointed rebuke.
"Man, I thought I got it hard, but the judge benchslapped the guy after me for just saying 'dude'."

First seen on the Wall Street Journal Law Blog "Federal Judge Slams Pennsylvania Lawyers"
by steegness October 02, 2007
 
2.
this is when you have to go before a judge and he slaps a bench warrant on you.
wow, harold went to court today and he got bench slapped by the judge.
by lindy1943 April 06, 2010