johnny-come-lately

She might take offense if some Johnny-come-lately thinks he can do a better job.

Morris now shared financial decisions with a woman, a female Johnny-come-lately. Imagine the eventuality of Morris's share of their fortune ever falling into such Johnny-come-lately hands. God forbid!

In a field increasingly populated with Johnnies-come-lately, Gittings is a Johnny-come-early: one only has to read this book to feel the depth and span of his knowledge.

He's a johnny-come-lately.