The Joker

"Shoot yourself in the head."

With a single command, you do what Batman couldn't do in years.

The Joker is a serial killer supervillain who killed hundreds of innocent men, women, and children.

Yet Batman would've simply arrested him and put him in Arkham. Joker would escape a few months later and kill more people.

You're an antihero so you don't bother with due process and finish the job.

The police won't be able to incriminate you because their forensics will find the Joker shot himself in the head with his own gun.

His official cause of death will be suicide, not extrajudicial execution.

The only person who saw what really happened is his henchwoman but you've special plans for her.