kicking a dead horse

1.Attempting to reopen a topic or subject that is already resolved 2.To waste time doing something that has already been attempted

"If you're trying to get back with Ryan, you're just kicking a dead horse. He got back together with Becky."

by Single Mingling Pringle May 11, 2014

Kicking the dead horse

Pointing out a dry joke or horrible pun after it has already fallen flat.

Teacher : Yeah check it out
Student : Ok I will
Teacher : Get it? Check it out, for the chess tournament
Student : Your kicking the dead horse sir

by NewfoundlandYeti October 19, 2009