Even a loser like George Costanza is mocking Anthony”Carlos Danger” Weiner.

“Seinfeld” actor Jason Alexander jabbed the penis-posting pol on Twitter yesterday tweeting: “Anthony Weiner plummets in latest poll . . . I believe the term is ‘shrinkage.’ ”

He was referring to a 1994 episode of “Seinfeld” in which his character is embarrassed when a woman spots his “shrinkage” after a swim.