Let me first say this, you seriously need to stop caring what others think of you or your car. I assume you are in high school. If so, allow me to give you this tiny bit of advice.
Right now, everything evolves around being "cool". You need to dress "cool", you need to act "cool", you need to look "cool", talk "cool", and drive a "cool" car. You know what? All of that ends the DAY you walk out of high school. Trust me on this one...ask anybody 19 years old and older. I am 33, and "cool" ended the moment I walked out of high school. I was "cool", and all the great things that went along with being popular were all gone. I couldn't rely on being popular to get what I wanted anymore. It sucked...hard. It was amazing to me how quickly and how drastically life changed the day I left high school. Your friends....kiss them good by. You might run into one of them every now and again...you will exchange "We should get together."s...and you never will. With the exception of one or two of your closest friends...you won't see most of them ever again.
This kid with the Stealth.....he is in for a suprise. His "cool" car isn't going to be such a status symbol any longer. He will just be another ******* in an old import...a dime a dozen.
Always remember that the next time someone says something stupid to you about your car. When school is over, none of it will matter.
Your car is not YOU. Your car is NOT who you are. It is a car...nothing more.
I wouldn't sell it if you like it. Paying out the nose for a newer car won't do anything for you...except make your wallet smaller. It's not like you will automatically gain this superior status with a newer car. You will just be the same guy in a newer car.
What you do with your car is your business. But the deeper issue is you letting some random douchebag get to you because he made some stupid ass comment about your car. Next time he says anything just tell him that you can run him over in your "POS" just as easy as any other car. Or better yet, tell him you have a nasty nitrous system under the hood, turn the car on and open your hood. When he leans over to look inside the engine bay, shove his head into your fan....try to get his shirt collar caught in a belt or something....then hold his torn up head against your exhaust manifold. That will teach him.
You know, on second thought....just tell him "you simply don't get it...do you?" and walk away. Let him think about that one for a while.
NOTE FOR THE LAWERS OUT THERE: I do not condone or suggest inflicting pain on another human being. Please do not follow any instructions to due so, as they are obviously intended as a joke.