- Who the hell are you?
- Western Union.

3 seconds sound clip from the Back to the Future Part II movie soundboard.

You can hear this line at 01:38:59.323 in the Blu-ray version of the movie.

Quote context

[...]

- Doc, do you read me? Do you read me, Doc? Come in. Doc!

- Oh, no. He's gone. The doc's gone.

- Mr. McFly!

- Huh?

- Is your name Marty McFly?

- Yeah.

- I've got something for you. A letter.

- A letter for me? That's impossible.

- Who the hell are you?

- Western Union.

- Actually, a bunch of us at the office were kind of hoping maybe you could shed some light on the subject.

- We've had that envelope in our possession for the past 70 years. It was given to us with the explicit instructions that it be delivered to a young man with your description answering to the name of Marty, at this exact location, minute, November 12, 1955.

- We have a little bet going as to whether this Marty would actually be here. Looks like I lost.

- Did you say 70 years?

- Yeah, 70 years, 2 months, 12 days to be exact.

[...]