cry over spilt milk	waste time feeling upset about sth bad that has happened and cannot be changed
fly off the handle	suddenly become extremely angry without a good reason
give sb a taste/dose of their own medicine	treat someone in the sam bad way they treat other people
give sth a miss	decide not to do sth that you usually do
grin and bear it	accept a difficult situation without complaining or showing how you feel
keep a straight face	remain serious and not laugh
keep your hair on	used for telling someone not to get angry or upset
kick yourself	be very annoyed because you have made a mistake, missed an opportunity, etc
let off steam	shout or do something that allows you to get rid of anger
let sleeping dogs lie	leave a person or situation alone if they might cause you trouble
never/don't look a gift horse in the mouth	if you are given sth good, you should not complain about it or not to try to find defects in it
up in arms about	angry and complaining about sth