make (one’s) bones

make (one’s) bones
 v.— «He was not only going to teach Gina [Feliciano] a lesson, Mr. Fama was going to make his bones that night…He was going to shoot someone.» —“Jury Considers Fama’s Fate As Judge Denies Defense Bid” by Patricia Hurtado Newsday (Long Island, N.Y.) May 8, 1990. (source: Double-Tongued Dictionary)