big-boy pants

Etymology
From.

Noun

 * 1)  Pull-up underwear worn by a boy during and after toilet training, as contrasted to the diapers worn during infancy.
 * 2)  A notional pair of trousers or underwear worn by a male when acting maturely.
 * 3) * 2011, David H. Hoffman, "Ugly election rhetoric" [letter to the editor], Suburban Life, 25 May 2011, page A8:
 * If Horwitz is planning on running for office again in the future (and it certainly looks that way), perhaps it's time he put on his big-boy pants and engage in civil discourse.
 * 1) * 2014, "Jewish Community Football League Playoffs and Championship!", The Baltimore Jewish Home, 11 December 2014 - 25 December 2014, Volume 1, Issue 21, page 19:
 * Even with a broken finger, Wach put on his big boy pants, wrapped his hand, and dominated on the offensive line all game.
 * If Horwitz is planning on running for office again in the future (and it certainly looks that way), perhaps it's time he put on his big-boy pants and engage in civil discourse.
 * 1) * 2014, "Jewish Community Football League Playoffs and Championship!", The Baltimore Jewish Home, 11 December 2014 - 25 December 2014, Volume 1, Issue 21, page 19:
 * Even with a broken finger, Wach put on his big boy pants, wrapped his hand, and dominated on the offensive line all game.
 * Even with a broken finger, Wach put on his big boy pants, wrapped his hand, and dominated on the offensive line all game.