Face the music - to be confronted to one's action; Since she betrayed me, she has to FACE THE MUSIC.
Raining cats and dogs - rains very hard; It's RAINING CATS AND DOGS as I peeked to the window
Fit as a fiddle - to be very healthy; You might be so sick right now, but you just need enough rest and sleep and sooner, you'll be as FIT AS A FIDDLE
Tickled pink - made very happy; The good news tickled pink her
Piece of cake - very easy; I thought the exam was hard, good thing, it's just a PIECE OF CAKE