a) I must have offended Rosie because she gives me the cold shoulder.
give somebody the cold shoulder: to treat somebody in an unfriendly way
b) I'm sure John has been talking about me when my back is turned.
somebody's back is turned: one are absent and not able to see what is happening
c) Liam is angry because Kate sold his old camera behind his back.
behind somebody’s back: without somebody’s knowledge or permission
a) Tom paid through the nose for his new camera.
pay through the nose (for something): to pay too much money for something
b) Christ says he didn't steal the money, but he lies through his teeth.
lie through your teeth: to say something that is not true at all