Unnecessary awkwardness annoys me.

After a long day at work tonight, the boys and I hung out by the lake, drinking beers and talking with a female coworker. Everything was cool and whatnot. At the end of the night, walking back to her car, she and I were walking side-by-side and she bumped into me, so I put my hand on her back for a second as we were walking. It seemed like things got weird and a bit awkward after that. I don't really understand why, but it annoys me that a good night had to end with something like that.