knock cold

knock someone cold 

1. Fig. to render someone unconscious by a violent blow. One swipe, and he knocked him cold. If you touch her again, I'll knock you cold.

2. and knock someone dead Fig. to put on a stunning performance or display for someone. (Someone is often replaced by 'em from them.) This band is going to do great tonight. We're going to knock them dead. "See how your sister is all dressed up!" said Bill. "She's going to knock 'em cold."

See also: cold, knock