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 he sees red mist, 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 I must have seen red mist because, the next thing I knew, I was being dragged away with bloodied knuckles.