When Henry came to Sherlock telling him about a gigantic hound wandering around Dartmoor, he was hooked on the case. He realised someway in the story that this hound was in actual fact a hallucination, and so John went into the lab, alone, armed only with a torch, to hallucinate and feed back to Sherlock what he was seeing. Except Sherlock told none of this to John: he couldn't. He merely locked him in a lab, scared for his life, and phoned him, asking to describe what he thought was about to brutally murder him. There might not have been another way to solve the case, but do you think your best friend would forgive you for doing a thing like that to them? When Sherlock found John, he was understandably furious. "It's okay," Sherlock comforted, as John shouted, "Nooo, it's NOT!" It's not okay!" It was another hilariously tactless move from Sherlock, and one that left John questioning their friendship.