Slender man's brother
The man that stands in the background of a porno and does not participate in the sex.
Kid 1: "I was watching a porno last night, and happened to notice this creepy guy just sitting in the background watching.."
Kid 2: "Oh yeah, we call those guys Slender man's Brother, I dont know what the deal is with those guys."
Kid 2: "Oh yeah, we call those guys Slender man's Brother, I dont know what the deal is with those guys."