The Free Dictionary says:
To help someone else, typically at their request. In this usage, the person being helped is stated between "do" and "a."
- Example: Hey, do me a favor and take these bags into the kitchen while I get the others from the car.
while, the Cambridge Dictionary says:
do me/us a favour! as an informal phrase, means:
Something you say in answer to a stupid and impossible suggestion:
- Example: "Why don't you tell the police what happened?" "Oh, do me a favour!"
These are two absolutely different matters, and I'm looking for a formal (Cambridge introduces this phrase as an informal one), and not something ambiguous (while different dictionaries have different explanations of it).
Is this expression frequently used in "formal situations" in my first example sense?
If not, then I wonder if there is any better formal and NOT ambiguous substitute for that in my first scenario.