So read up 'bout how I used to get beat up
Peed on, be on free lunch and changed school every 3 months

from Eminem – Who Knew Lyrics on Rap Genius

Meaning

Even though everyone blames Eminem for negatively influencing society with his accusingly distasteful lyrics and purportedly inappropriate subject matter, they seem to ignore the basis of the problem.
He states these problems to be all the harmful influences in the world other than him. He brings into the fact that kids and people have always been ruthless, even before he started rapping, so obviously it’s not his fault.

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