With the D&D episode, the entire point was that the group, as well-intentioned as they were, did nothing to help Neil. It was Pierce's bullying, and inadvertently revealing of his feelings of loneliness and exclusion, that made Neil realize he wasn't alone, and moreover could help Pierce. This continued through to the documentary episode, when Pierce's feelings of rejection went to their extreme, and the group realized that perhaps they haven't been as nice to him as they should have been. Ever since that episode, he's been with them much more presently, so he's felt more accepted, and thus hasn't needed to act out in any way.