How is “while you're at it” used?

In Monty Python's The Meaning of Life (1983), one line is: “Oh, and while you're at it, you'd better get a doily.”

Which movie is “while you're at it” from?

The clip at the top of this page is from Monty Python's The Meaning of Life (1983).

used to suggest that sb could do sth while they are doing sth else

Heard in 17 moviesPlay Idioms

Oxford100% of films
used to suggest that sb could do sth while they are doing sth else
While you're at it, can you argue self-defense?

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

Oh, and while you're at it, you'd better get a doily.

Said in 8 films · #1