Knock somebody dead
Definition 1 of 2
Pro Tip 1/3Positive Impression
Use when someone does something so well it astounds others. 
Lisa's speech was so compelling, it knocked everybody dead.
Pro Tip 2/3Colloquial Usage
Common in casual speech or writing, but not in formal situations. 
His jokes aren't just funny, they'll knock you dead!
Pro Tip 3/3Performance Context
Often used to describe outstanding performance in arts, sports, or business. 
With her flawless dance, she knocked the judges dead.