What's more important to me is how he responds to it now, as a "man" and as a candidate to lead the entire country, and how he views his actions. His "I don't remember", "well I apologize IF anyone was offended" response was weak and cowardly, or worse, oblivious. It shows a lack of courage for taking responsibility for past mistakes, even ones you might consider "excuslable".
The fact that he even claims not to remember is disturbing, because his classmates remembered, and the victim sure rememberd, but to him it was probably "just another prank", and why should he care about anyone besides himself? He leads a charmed life, who cares about the kids he bullied? Out of sight, out of mind.
What's not great for him is this is in line with the widely-discussed treatment of his dog - dog was miserable and terrified strapped on top of a car, but he didn't give a shit and just sprayed him down. And he doesn't understand what all the fuss was about.
As leader of the free world, he'd be responsible for the welfare and well-being of millions of people, and his decisions could destroy the lives of people in countries thousands of miles away. If he is unable to show remorse or empathy for his personal decisions, or be honest and take responsibility for them, how will he respond (or will he respond at all) to the plight of the poor, the disenfranchised, minorities, people in third-world countries - people he will never see face-to-face, but who would depend on him just the same. If they're out of sight and not within the circle of his charmed life, will they matter to him, or will he even remember they exist?
I could respect him if he took responsibility for the incident, made a statement that bullying was wrong and unexcusable whether in the past or today, and that he learned from the incident. But it seems he's still the same privileged prep school boy who doesn't understand why "other people" get offended when he has a bit of fun.
I don't think President Obama has been perfect, either, but the contrast in the President supporting same-sex marriage and expressing his moral convictions, even at the cost of votes, vs. Romney's cowardice and lack of empathy is pretty stark.