what does being too main stream mean?
Well mainstream means something that's very popular, everyone knows what it is, everyone's seen it, everyone's done it, etc. For example: "Ew, I don't like One Direction, they're way too mainstream for me."
Being so popular that nobody notices anymore.
It means cliche with an accent on the e
It means youre just basic. Not unusual or novel anymore. It's popular.
It means the the person may lack individuality and creativity.
Mainstream means popular, or overdone.