The article I linked to includes the following passage:
Well, then. I think that says it all. He's got amazing talent, this kid. Unfortunately, just as I suspected, he's been coddled and spoiled and it's affected how he treats other people. He really needs to mature in personality before he belongs in Harrisburg, let alone even with Potomac. I love his upside, but I'm not a big fan of his bratty personality. He'll have to realize he's not entitled to everything automatically and he'll have to work his way to the top just like everyone else before he can actually advance. Remember, Bryce, this is a mental game, too, and mean people get ostracized and disliked. And that does not bode well for you.
There was this from Baseball Prospectus before Harper was drafted: "It's impossible to find any talent evaluator who isn't blown away by Harper's ability on the field, but it's equally difficult to find one who doesn't genuinely dislike the kid.
"One scout called him among the worst amateur players he's ever seen from a makeup standpoint, with top-of-the-scale arrogance, a disturbingly large sense of entitlement, and on-field behavior that includes taunting opponents."
"He's just a bad, bad guy," one front-office official told Baseball Prospectus. "He's basically the anti-Joe Mauer."
UPDATE: Here is some video of the incident. It makes me wonder if the pitcher saw Bryce Harper leaving his helmet at home plate as an affront, as he was walking away without it after dropping it at home. It's very hard to see what's happening here, so I can't determine if this video tells me who's really at fault here, Harper or the opposing pitcher. Either way, though, this is at least entertaining. The strikeout comes around the 1:25 mark.