Quote from PokeCanada
Just head to:
Options>Video Settings>Details>Show Capes then select off. That will turn off ALL Optifine Capes but shouldn't take off your legit cape.
Quote from Shady7s
This does not work,it will disable both.
I had to message sp614x and ask for it to be disabled. He says he is working on optifine.net accounts so people can manage their capes.