I don't think there is an Italian equivalent for this definition
"In American usage, bubba is a relationship nickname formed from brother and given to boys, especially eldest male siblings, to indicate their role in a family. For some boys and men, bubba is used so pervasively that it replaces the given name. The nickname may also be used outside the family by friends as a term of endearment."
Cafone, as Ditrina ( Wikipedia ) said, is the Italian equivalent of
"Because of its association with the southern part of the United States, bubba is also often used outside the South as a pejorative to mean a person of low economic status and limited education."
In the Army we have Nonno (grand father) which is the senior soldier
"Bubba may also be taken to mean one who is a "good ol' boy." In the US Army and Marines, bubba can mean a lay soldier, similar to grunt but with connotations of endearment instead of derision (e.g., "Can you make that device easier to work with, 'cus every bubba is gonna have to use it.")."
Grassone is the equivalent for
"At times it may be used as a term of endearment (or in an insulting sense) for a person, especially a man, who is overweight or has a large body frame."
No idea of any possible Italian translation for
"In popular culture and prison slang, it is often joked that new male prisoners will be obliged to share a cell with a large, physically powerful inmate called Bubba who will become forcibly sexually intimate with them."
