Why does smart = nerd?

As a type of punishment for doing poorly, on purpose, in reading, I made my 6th grader take a summer school math class. He can read and is a good reader, also somewhat enjoys reading. So because I knew this I made him take math. He does not like or do well in math, but got a mediocre grade during the year after lots of struggling. So anyway, he 'kind of' liked the math teacher over the summer (not the same as the school year, thank GOD). On the last day of school I asked him for his grade card and he gave me that famous disgruntled face and that weird sound they make to go with it. My heart sank and I feared the worst. It took asking twice for him to get me the grade card (did I mention ADHD?). He got an A. He got an A. He was embarrassed he got an A. We have struggled with this the majority of his school career. He makes comments that the smart kids are nerds and butt kissers. He thinks when you do well it somehow makes you uncool. I don't know where he gets these ideas. My husband and I both are pretty smart, we think. We both have graduate degrees and work for the public school system. Heck we're 'nerds' apparently. So the 6th grader knows all, of course. He limits his success in school to aid in his increasing social status. He is quite handsome and funny and smart(how could he not be both, he is mine)but this attitude concerns me. How do I get rid of it? How do I make him see that smart people are not nerds. Smart people go to college and get better jobs and better spouses and better cars/houses/etc.....
My husband struggled with this as a teacher in an urban school district. Kids didn't try to succeed in fear of loosing 'face' with their friends. We live in suburbia, folks. Trust me no one will attempt to beat him up for making an A in math. Ugh, I hate adolescents.