Arthur's tweet expressing fear of !UP shows that he is feeling anxious and apprehensive. He is clearly scared of whatever !UP represents and the three consecutive emojis of a scared face further expresses the intensity of his fear. It is likely that Arthur is afraid of the unknown and the uncertainty surrounding !UP. He may also be worried about the potential consequences of !UP, whatever it may be. Whatever the source of his fear, it is clear that Arthur is feeling overwhelmed and scared.