Or a Dumbocrap.
‘Moonbat’ is the ultimate designator. Even the liberals admit it’s peerless. The closest they have is ‘wingnut’, but it doesn’t pack the same wallop. Once you’ve called a leftist a moonbat, you’ve pretty much covered all the bases. I even caught a DU thread once where they were trying to come up with a word for us that carried the same pejorative impact, but they just couldn’t do it. Kind of nice to know, isn’t it?