fair do's

Informal, often used in UK. Something you say when something is reasonable, similar to fair enough.

"Sup"
"Nothing much, you?"
"Vibin"
"Fair do's"

(Doctor Who)
Wilfred: You know, I don't understand half the things you say these days.
Donna: Nor me.
Wilfred: Fair do's. You've had a funny old time of it lately.