Green’s Dictionary of Slang

1. (US black) immature, unpleasant, stupid, bland.

1969		S. Greenlee Spook who Sat by the Door (1972) 15: One of those diddy-bop niggers from Chicago had almost stolen his present wife.
1979		S. King Long Walk in Bachman Books (1995) 289: You and your diddy-bop friends.

2. (US campus) unattractive.

1964

in Current Sl. (1967) I:4.

3. stylish, sophisticated.

1974		(con. 1960s) R. Price Wanderers 138: [H]he turned on his record player [...] and practiced dancing [...] as long as there was some kind of hip ditty bop noise [...] he was safe.
1983		R. Price Breaks 156: His act, an urban ditty-bop routine, was too much like my own adopted persona.

4. (US drugs) second-rate.

1979

High Times Jan. 8: I want to have coke up my nose, not this diddly-bop candy.