Can't think of a less intimidating nickname than "Orchid Man" Carpentier. Also "Slapsie Maxie" Rosenbloom doesn't sound too dangerous!
Pernell "Sweet Pea" Whitaker Felix "Tito" Trinidad Bobby "Boogaloo" Watts "Sugar" Ray Robinson Ray "Boom Boom" Mancini Antonio "Kid Pembelè" Cervantes Bobby "Schoolboy" Chacon Carl "The Cat" Thompson Saul "Canelo" Alvarez Meldrick "The Kid" Taylor Alfonso "Peppermint" Fraser
- Lance "Goofi" Whitaker - Jim "The Cinderella Man" Braddock - Willie “The Worm'' Monroe (Well, it depends on the worm, see e.g. Frank Herbert's Dune saga...) - or "the Louisville Lip" for Muhammad Ali doesn't sound too intimidating to me. BTW., I think the coolest nickname had Willie Pep "Will o' the Wisp" (short and appropriate).
Any fighters with the nickname "Baby". Sam "Boston Tar Baby" Langford Baby Arizmendi "Baby" Jake Matlala Anthony "Baby" Jones "Sugar Baby" Rojas Baby Luis "Baby Faced Assassin" is an exception though.