It refers to the belief that gingers have no soul and worship the devil. Also, the fact that they do nothing but cause pain and evil on others.
Chris: Oh nothing just some satanic chants... My deadline is tomorrow; I have to eat the souls of at least 12 people.
Johnny: You fucking devil worshiper!
Phillip:"That why Terrence,that's why"
T & P: "ahahahahahaha"
Terrence:"you filthy fucka"
Terrence:"This is for all you devil worshipers" *farts*
T & P:"Ahhhh-hahahahahahaha...you smell like ASS!"