A person, who upon wearing a satin devil costume, or adorning horns becomes 'Diabolical'. Their behavior is somehow altered, by the costume. Otherwise, they are your typical God fearing Christian, with an adverse reaction to the Devil. There are many behaviors which fit this label, which is expanded to Satin-ism. The -ism, suggests a practice, or adherence to beliefs. The Satinist, is not just wearing a costume playing a part, it invokes in them mischievous thoughts and behavior.
Bill (wearing costume): I am EVIL, mu ha ha ha ha!
Susie: Oh my! Aren't you afraid of offending God?
Bill: NO! I am the Devil!
Susie: Ok Bill, see you at church on Sunday. You Satinist!