It really annoys me when I come across people who complain when their grades fall below their expectations and those who exalt themselves when they get high grades and then brag about it.
C'mon. I mean, it's good to be conscious about your grades. It means that you are giving value to your education, but, please compete with yourself and not with your other classmates. Do it on purpose, to make yourself better and not just to impress others. And also, be nice and try not to brag about your high grades. You don't have to announce it to the whole world, "Hey! Look at my grades! They're way too high! Oh, I must be a genius." Keep it to yourself, dude. Let others have their jaws dropped, do the talking and tell you that you really are intelligent.
On the other side, I also don't like it when people overuse the idea that grades do not define a person. Some use it as an excuse to back up their low grades and that is because they did not do their best in school in the first place. Well, it's true that character, and not grades, defines a person. However, please stop from using it as an excuse for your failing grades.
It's nice to be grade-conscious and challenge yourself to be the best student that you can be. After you've done your best and are now reaping the sweet results of your hard work, don't shout it out. Let others become proud of you. And also, don't use trite phrases as excuses for your low grades that in the first place you know you have done nothing to pull them up. After all, you deserve whatever is the result of the amount of effort you give. :)