50 Cent DISSING Jay-Z? -- Says Rappers Shouldn't Be Sports Agents

Seems 50 Cent is trying to pick another fight with Jay-Z -- 'cause last night he told TMZ that rappers "should never" become sports agents ... EVER ... with one, small egocentric exception.

Fiddy doesn't exactly call out Jay-Z by name when we asked the question outside of Craig's in Hollywood -- but c'mon ... we all know who he was referring to.

FYI ... Jay's sports agency, Roc Nation Sports, is growing fast -- signing big stars like Yankees 2nd baseman Robinson Canoe and NY Giants receiver Victor Cruz.

But RNC came under fire last month ... when the NFL Player's Association launched an investigation into the agency to see if Jay violated recruiting rules in his pursuit of NY Jets QB Geno Smith.

Still, 50 says there is ONE rapper capable of conquering the sports agency biz ... a rapper who's been shot 9 times, happens to be friends with Eminem and may or may not be himself.