This is highly anecdotal, but when I was younger (from ~5-15 years ago), I noticed I was far more likely to have people start fights* with me when I was in a good mood and enjoying myself. Yet this never seemed to happen when I walked around with a bit of an angry look in my eye, like I had been having a bad day and was just waiting for someone to start something. I even informally experimented with it, sometimes approaching people in a cheerful, happy way, and other times approaching them like I was in a really bad mood. Men seemed to treat me much better when I was faux-pissed, and much worse when I was in a good mood. The authors didn't experiment with this (that I could tell), but I'd hypothesize that males have the same reaction towards happy expressions in other males - they don't like them and it initiates aggressive tendencies.
*You might ask why I was getting into fights in the first place, and all I can say is that high school and college are rough and most of the population doesn't seem to be as sophisticated as the typical HN reader.
*You might ask why I was getting into fights in the first place, and all I can say is that high school and college are rough and most of the population doesn't seem to be as sophisticated as the typical HN reader.