According to this Boston Herald article, U.S. Representative Patrick Kennedy described the candidacy of Senator Scott Brown as "a joke." Brown was recently elected to fill out the remainder of the senate term of Patrick's father, Edward Kennedy, who died in office.
Republican Brown won a substantial majority of the votes in heavily Democratic Massachusetts. Such performance by a politician is no joke. Had Brown lost by a wide margin, that candidacy would have been a joke.
What Patrick really has done is criticize the judgment of his home state voters, never a wise move in politics. I expect he will regret this ill-advised remark.