Most of the time, I know enough about human nature that I can sort of manage my own expectations. Really, the problem is not how other people react, it is when they don't react the way I was expecting them to that is ultimately the problem. I had plans with friends that just turned out to be a lot harder and a lot more frustrating for me than I would have expected. After I let go of my attachment to the outcome, it became easier. It didn't become EASY, just easier.
I also worked most of the day, so maybe it would be best not to combine the two - day at work and a "project" type outing with friends. Sometimes, after work, you just need a bit of normal.
It all ended well and I hope everyone had a good time. I just exhausted myself with worrying about it all and trying too hard.