We hate to come back to the topic of terrible sports nicknames, but in the case of "Slapsie" Maxie Rosenbloom, it's pretty hard to avoid. Yes, Slapsie. Sigh.
Rosenbloom, who became world oxymoronic light heavyweight champion in 1930 (and then again in 1933), was a prolific fighter with close to 300 bouts to his name. His got the nickname because of his distinctive style: he not as much punched, as he... slapped.
Still, that slapping was good enough to win time and again. Alas, it wasn't for the National Boxing Association, which stripped Rosenbloom of his title in 1934 because they deemed his style improper. (Antisemitism? We bet there was antisemitism too.)
After retiring from boxing, Rosenbloom became an actor, appearing in at least 80 movies and TV shows. He parlayed his tough guy persona into... slapstick comedy.
The nickname might have be terrible, but it definitely worked.