Dumbest thing I've probably done was to bring my (now ex) girlfriend on a trip even though I knew the relationship was pretty much over. I thought it might help in saving things but all it ended up doing was costing me a lot of money. Less than a month later, we were broken up and I was a bit less rich.
You live and learn!
I knew a couple who had booked a holiday together but kinda split up a month or so before the trip but went on it anyway. It didn't turn out very well. The two week holiday pretty much turned into seeing who could sleep with the most people haha. The situation would probably make a pretty funny film .