set (one's) back up(redirected from set their backs up)
set (one's) back up
1. To be or become angry, hostile, defensive, or irritable. John started setting his back up when his parents brought up the subject of college again.
2. To cause one to become angry, hostile, defensive, or irritable. Election season always sets my dad's back up. Few things set my back up like hearing about a poacher killing an endangered animal.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.