We must do lunch one day!

Isn’t that the most convenient and nice little phrase to say just being polite and without meaning it.
“We must do lunch”, or “Call me next week”!

But just saying that without meaning it can cause you problems here in Finland. People here take your word for more seriously than just politeness. Saying a courteous non-committal “we must do lunch” the Finns really respect that you have made a promise to have lunch and they expect you to have the lunch with them!

So keep in mind what you say and how you say it, and also be in time for your lunches.