A member of a popular croud with no soul, usually found at a middle school or highschool. They have zero taste in music or movies, they use these things as a way to get more popularity. They make tee-shirts that say "(insert event here) is life" or "I Heart (insert event here)" usually the event would be viewed as uncool so they get a large group of people to pretend it's cool so that they can all feel cooler.
anyone with a soul hates mainstreamers except for the head mainstreamer because they have control of the entire mainstream body
Dang those dumb mainstreamers made stupid bowling t-shirts and bragged about it for ever.