It's the good girls who keep the diaries; the bad girls never have the time.

Bankhead’s quip plays on the contrast between “good” and “bad” girls as social types: the “good” girl is imagined as orderly, reflective, and domestically contained—someone with leisure to record her days—while the “bad” girl is figured as too busy living impulsively (or scandalously) to write anything down. The joke also winks at celebrity self-mythmaking: diaries are associated with confession and respectability, whereas Bankhead’s public persona traded on speed, excess, and irreverence. The line’s staying power comes from its compact inversion of moral judgment into a comment about time, experience, and who gets to leave a written record.

“The good girls keep diaries; the bad girls never have the time.”
“It’s the good girls who keep diaries; the bad girls don’t have the time.”