The level of awesomeness it takes to kill a man. The most common example of this can be seen in Tobuscus' Assassin's Creed Brotherhood Literal Trailer on Youtube. The event in which Deadly Awesome is reached, Ezio Auditore walks through a crowd and kills a guard "with his awesome".
Guard says "Stop!" just kill him with your awesome. (This is an example of when Deadly Awesome has been reached)