How is “be lookout” used?

In This Is the End (2013), one line is: “There's a lookout.”

Which movie is “be lookout” from?

The clip at the top of this page is from This Is the End (2013).

Idiom

used to say that you do not think sb's actions are sensible, but that it is their own problem or responsibility

informal · British · Heard in 51 movies

be sb's lookout
used to say that you do not think sb's actions are sensible, but that it is their own problem or responsibility
If he wants to waste his money, that's his lookout.

Definitions from the Oxford Advanced Learner's Dictionary, 9th edition

There's a lookout.

Said in 8 films · #1