Once by Goku, three times on Namek (Racoome, Zarbon, and Frieza), once by Cell, and once by Buu. Not to mention the beatdowns he got in the movies too.
I think he's a close second on brutal beatings received behind Krillin.
ETA: Can't say I felt sorry for him. He did it to himself most of the time.
This post was edited on 7/24 at 10:22 pm