"I'm so mean, I make medicine sick" boxer (3)
I believe the answer is:
ali
'i'm so mean i make medicine sick boxer' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ali that I've seen before include "Son-in-law to Muhammad" , "Old fighter" , "Cassius Clay became Muhammad ..." , "Former boxing champion" , "Muhammad ___ (or MacGraw?)" .)