Define

C, D

These letters don't define me.

They say you fail a test?

You'll grow up to be a pest.

But these letters don't define me.

Go to college, be somebody.

But those letters don't define me.

A,B

These letters define you as smart?

Smart?

Grpwing up, smart was knowing, 

the difference between right and wrong

And just because these letters are different.

Don't mean these letters define me.

M,E 

These letters define me.

F is fail, fail is like a annoying tail, always there and drags behind you everywhere.

But this letter doesn't define me, they say these letters define you.

But nothing can define you, define me, but me