How do you react when someone accused you of a sin you did not do?

when people accuse of something i didn't do or just accuse me of something i am not or just think of something i am not, of course i'd be pissed. but as long as i can tolerate it, i'd ignore it. but when it comes to the point that i can't let it pass anymore, i kind of do the thing or act the way they thought i did or they thought i was. ^__^;; i know its the best thing to do and i usually try my best to stop myself from doing it. sometimes there has to be someone to knock some sense to my head and prevent me from being like that. LOL

Back when I was in school, I stayed back during break time to clean up the classroom as my school had this competition where they'll crowned the cleanest and dirtiest classrooms? Although I was stupid in doing that, I didn't want my class to win the "Most Dirtiest Class" award just because my classmates were lazy. And do you know how they thanked me? One of the girls lost her stupid purse and claimed I stole it by pretending to stay in class and clean up the classroom. Technically in my school, whoever kisses butt the most tend to have the teachers siding with them. Although my teacher refused to believe I did such a thing, these girls spread rumours around the whole school that I steal for a living, they even said that whatever I had on me, like my school bag, schools, socks, watch, stationary, etc, was stolen!! Although "truth shall prevail", but in my case, the truth came way too late as my reputation had gone down the drain thanks to these girls. Definitely I hated them and I did wished I had do something about it, maybe retort back or gave their "ringleader" a tight slap on the face, but I was really too meek to do anything. Worst of all, I have no friends in school to stand up for me when such a thing happened. But the good part about it, throughout the 4 years in school, these girls proved to everyone that they are no innocent saints like what they pretended to be. And was I glad that everyone saw them for who they really were and also of the fact that everyone forgot about the "stealing" episode. Whether you react to accusations or not might not necessarily do any good, it's more of a matter of how you would handle the situation. If you keep quiet, people will say you are guilty. But if you retort back, people will also say you are guilty. In a sense, reacting is a double-edged sword.

most people i know are always the ones that are the more agressive when it comes to making a statement about another even more in the situations of accusing someone with some kind of bad deed they might not have done.... but theres two things that i need to think of in making the truth seen...first stay calm...and second calm the person who is accusing me of this misdeed...