Of course it's acceptable. Understandable, too! And let me add that it's completely possible that them not smiling is really unrelated to the loss, because if you look at the picture another user posted, even winners don't always smile.No need to take the statement as a total absolute. The amount of people ripping on these boys is baffling. They're not smiling. So what. People want to assume it's because they lost to a girl. It's totally acceptable for somebody not to smile when they've lost.
What I'm arguing against is the toxic notion that everyone who didn't end up in first place not smiling is how it "should" be if they want to be winners.