I went abroad for a wedding with a married couple and another single person, Chris. The couple paid for themselves and it was decided that Chris and I would split our costs - accommodation, food, petrol - down the middle.
My attitude in this situation is (perhaps too) relaxed. I'm like 'you paid for dinner last night, so I'll pick up the bill tonight'. In my view of the universe, it all works out about even, give or take.
A few days into the trip, the couple told me, on the quiet, that this comme-ci-comme-ca would probably not go down well with Chris, who was notoriously tight. But Chris didn't say anything so I didn't really think about it.
At the conclusion of breakfast on the morning I was leaving, Chris said, "So, before you head for the airport, we need to settle up."
I thought, "Hello. Here we go."
Chris said, "I've been keeping track of expenditure and if you pay for this breakfast, then..." A calculator was produced, plus a note of expenditure to date. Chris looked at the bill for breakfast and tapped in the numbers "...then, umm, hang on. Yes. I owe you three pounds twenty-nine." Which precise sum was then counted out in cash and pushed across the table towards me.
"Chris, it really doesn't matter."
"No, no - we agreed we'd split the cost. I owe you three pounds twenty-nine."
Tight, yes, but very, very fair.