Mob knows he’s oblivious, and he’s used to pretending he’s not feeling anything. So his poker face is unbreakable, and he’s aware of that as well. He pretends to not realize that Reigen isn’t psychic, and he knows everyone around him will believe it; all he’s gotta do is wear the neutral face he usually wears and I think that’s so funny. Like he’s been punking Reigen for YEARS. Mob isn’t the one that’s been fooled in that situation, Reigen is, and Mob has fun with it.
Like…you CAN’T tell me that Mob really doesn’t realize that Reigen is a fraud. From the beginning, he’s like “oh man, this one seems really dangerous…a normal person might die…” regarding spirits that he could exorcise effortlessly. And Reigen is genuinely like. Sweating.