The idiom knock them dead or knock ’em dead is considered to be of American origin. We will examine the meaning of the idiomatic phrase knock them dead or knock ’em dead, where it came from, and some examples of its use in sentences.
Knock them dead or knock ’em dead is an encouragement to do something well, to project an impressive appearance, to enjoy success. The term knock them dead is often abbreviated to knock ’em dead, in a humorous manner. The phrase came into use in the 1890s in American vaudeville. Vaudeville is a type of live variety entertainment that was popular until the advent of the motion picture. Originally, the term knock them dead or knock ’em dead was used to wish a performer luck. It seems that the relationship between a performer and his audience is often seen as adversarial or combative, hence the use of terms such as knock them dead or knock ’em dead, slay them, or kill them, all referring to the audience. Phrases related to the idiom are knocks them dead, knocked them dead, knocking them dead.
Examples
WWE’s announcement also comes after the two sides have spent months trading both subliminal and overt disses, from Cody fancying himself as an “Attitude Killer;” to Triple H calling AEW a pissant company; to Jon Moxley’s viral scorched-earth interview against WWE; to Seth Rollins vowing to “knock them dead;” to The Elite invading Raw that one time in Ontario which resulted in legal threats from WWE. (Forbes Magazine)
Yes, your sugar skull cookies and cookie haunted mansion may impress your guests, but your severed toes in a blanket (AKA pigs in a blanket) will knock them dead. (Woman’s Day Magazine)
So get ready to drop everything, kick up your heels and experience a knock ’em dead season that’s practically perfect in every way. (Broadway World)