1. All work-related discussion should take place in formal meetings.
and
2. No non-work-related discussions should ever happen in the workplace.
?
If you are having a discussion with your boss don't bother him when he is on a break, book a meeting.
I agree with parent poster in large orgs but in orgs where the founder eats lunch with you that level of formalness is awkward
"I'll grab a donut from the store across the street. Does anyone else want something?" - "No, we don't because YOU'RE FIRED."