It's one of those removed-from-ordinary-experience studies, but it's interesting that high-testosterone people get reinforced by frowny faces. Low testosterone people don't.
This might answer a question I've wondered about--there are people who get absolutely desperate at the suggestion that they shouldn't insult people, and I've wondered what the drive might be.
Unfortunately, I can't find my most recent perfect example--a fellow who couldn't find a picture of police breaking laws at a Washington DC police convention, so he settled for a picture of a fat policeman which he was delighted to mock. No argument from kindness or practicality (after all, his main point was police unlawfulness) would convince him that he should give up the pleasure of being nasty to a stranger.
Here's a slightly less good example: John Scalzi is absolutely committed to saying that teen writing sucks. He comes up with pretty reasonable caveats, but he will not drop the insult. He loves it too much. Will Shetterly makes the excellent point that getting good writers is more important than selecting for hardiness--and they aren't the same thing. This doesn't register.
Obviously, this isn't just about facial expressions--there are plenty of people who get their satisfaction from being insulting online. I expect that just imagining that someone's feelings are hurt is frequently enough.
The link about the study was posted by andrewducker in these comments.