French phrase
Je préférerais que vous ne ~ pas.
Meaning
I would prefer you not to ___.
When to use it
Politely asks someone to refrain from an action. It is softer than a command but may sound reserved.
Example dialogue
Je préférerais que vous ne fumiez pas.
I would prefer you not to smoke.
D'accord, je vais fumer dehors.
Okay, I'll smoke outside.