A couple of more thoughts about a scientific study which found a correlation between testosterone levels and being reinforced by seeing a frowny face.
I don't think it's just about testosterone. There are top athletes who are known as reliably friendly and kind. I'm guessing here, but I bet it takes above average testosterone to build the muscle mass needed for many sports and to be interested enough in competition to play at high levels. I bet there are at least other hormones in play. It also might be possible for early training to affect a positive response to frowns--it might be more like repression than actually making it go away, though.
It's a little more complicated than a response which is always there or not. In general, I don't like hurting people's feelings, but there have been times when I was in an abstracted bad mood, and strangers have told me to smile. I'd snap at them, see their faces fall, and cheer up immediately, like flipping a switch. On one level, this is funny--after all, they did want me to be happy. They just weren't expecting to pay a price. On the other hand, it spooked me quite a bit--was there some sort of lurking nastiness in my psyche? Maybe not--maybe it's just a testosterone(?) surge from being exposed to presumptuousness from a stranger when I'm already in a bad mood.