How to revenge on clare:
Step 1: Become popular. It is not as hard as you think. Learn how they think, start playing sports, make friends with higher up people in the food chain. This is entirely possible, I did it myself without even trying. (of course elementary school is a bit easier)
Step 2: Clare is there with you. Ignore her, increase your wit and shoot a comeback whenever it's needed but don't publicly hate her.
Step 3: She stops after getting no reactions. Continue to ignore her, but after a few weeks if she is near you make light conversation. Leave with some heavy chick-flick line.
Step 4: Win girl's hearts. Now, if you actually find the girl for you at this point, just stop here. Your success is all the revenge you need. But if none of the girls are for you, leave em. Turn to Clare, ask her out. This has to be timed correctly.
Step 5: Date for a few months. Make you her sun and moon. She MUST love being around you. GF and BF status. Now if you still have feelings for her you can stay here but you have to leave eventually because you know about the torment she is capable of.
Step 6: Bring her to a party. Say "everybody, i'd like to say something about clare, my girlfriend" but make it sound kind and loving. Begin a speech that sounds wonderful, but twist it into all the truths about her. She will be so shell-shocked she will have no time to reply. Make her run out of the party crying, because if YOU leave, people will console HER. If she leaves people will be more likely to take your side because you exposed her. Spend the rest of high school ignoring her, not making her life bad, just ignoring her. Hopefully she will have gone down the chain.
An optional thing would be to get some dirt on her for the speech, or whenever she comes up in conversation.
tl;dr break her heart.