i already went over who started it!! It was in my earlier post! the underground comic BILLY KLEIN first started this saying!!

I'M JUST SAYIN'!!

This saying is widely used in the state of Michigan and seems to be
getting more popular with the rest of the world! The saying is the
equivalent of the old New York saying- "forget about it!" It was
first originally invented and used by the underground comic
sensation BILLY KLEIN of BURT, MICHIGAN, USA. He loves others to
use it in their everyday conversations, but definitely wants
everyone to know it was him that started saying it and using it
in his shows!!