To fall into a state of extreme anger, excitement, or competitive arousal, such as might cloud one's judgment or senses. Primarily heard in UK. Their striker isn't the most consistent player on the pitch, but once the red mist descends, you had better get out of his way. I'm not sure what happened. I was at the pub having a pint, and then someone insulted me, and I guess the red mist must have descended, because, the next thing I knew, I was being dragged away with bloodied knuckles.