Because if you ain't a great actor, you're a bad actor, and bad acting is bullshit in this job.

4 seconds sound clip from the Reservoir Dogs (1992) movie soundboard.

You can hear this line at 01:06:58.566 in the Blu-ray version of the movie.

Quote context

[...]

- Do right by him. He's a good guy. I wouldn't be inside if it wasn't for him.

- No. No, no, no, no. Long Beach Mike is not your fuckin' amigo, man. Long Beach Mike is a fuckin' scumbag. He is selling out his amigos. That's what kind of a nice guy he fuckin' is, all right?

- I'll take care of his fuckin' ass, man, but you get that lowlife scumbag out of mind and you take care of business, you hear me?

- Gone.

- You use the commode story?

- What's the commode story?

- It's a scene, man. Memorize it.

- A what?

- Look, man, an undercover cop's gotta be Marlon Brando, right? To do this job, you gotta be a great actor. You gotta be naturalistic. You gotta be naturalistic as hell.

- Because if you ain't a great actor, you're a bad actor, and bad acting is bullshit in this job.

- What is this?

- That's an amusing anecdote about a drug deal.

- What?

- Something funny that happened to you while you were doing a fuckin' job, man.

- Damn. I gotta memorize all this? There's over four fuckin' pages of this shit here!

- Just think about it like it's a joke, all right? You memorize what's important, the rest you make your own, all right?

- You can tell a joke, can't you?

- No.

- Pretend you're Don Rickles or some-fucking-body and tell a joke, all right?

[...]