The actor/musician was performing at Harrah's casino in Atlantic City, New Jersey at the weekend (03-04Jan10) when one member of the crowd pushed his way to the front row and accosted Grenier.
According to the New York Daily News, the man threw his drink over the star before shouting, 'You suck, Grenier!'"
He was then escorted out of the venue.
A source tells the publication, "Adrien looked shocked. Security came running up to the stage and had the guy removed."