do (one) a favor

1. To help someone else, typically at their request. Sometimes used sarcastically. Hey, do me a favor and take these bags into the kitchen while I get the others from the car. A: "Correct me if I'm wrong, but that sounds like an intern's job." B: "Just do me a favor and clean up the files, will ya?" A: "Hey, can you do me a favor?" B: "Sure, what's up?" A: "Can you hold the door open for me?"

2. A request for someone to stop doing something bothersome or annoying. Can you please do me a favor and take your loud music somewhere else? I'm trying to sleep! Look, I know you want to help, but do us a favor and just stay out of our way. Do us all a favor and get lost, creep!

3. A response to a statement that the speaker finds ridiculous or stupid. ("Favor" is usually spelled "favour" in British and Australian English.) Primarily heard in UK, Australia. A: "Katie seems nice." B: "Oh, do me a favour—she's one of the cattiest girls in school!" You, the night owl, are getting up at 5 AM tomorrow? Ha, do me a favour! Do me a favour—I'll believe that one when I see it!

do me a favour

used as a way of expressing brusque dismissal or rejection of a remark or suggestion.

1993 Merv Grist Life at the Tip Do me a favour, Webley couldn't even pass a mug of tea across the counter last season, let alone pass a ball.

do me a ˈfavour

1 (informal) used when asking somebody to help you: Do me a favour and answer the door, will you?
2 (spoken) you can’t expect me to believe that: ‘It’s worth £2 000. The man in the antique shop told me.’ ‘Do me a favour. It’s not even worth £200.’