Wolf in sheep's clothing.

For example:

"I don't trust him, I think he's a wolf in sheep's clothing." To pretend to be harmless when you are really dangerous.

Hot under the collar.
For example:-
"She got very hot under the collar when I told her someone had scratched her car." To be very angry.

Dressed to kill.

For example:

"She had bought a new outfit and was dressed to kill." To make yourself look really good by wearing your best clothes.

Fit like a glove.

For example:

"The dress fitted her like a glove." Fits very well.

To be hand in glove.

For example:

"They make a great team. They work hand in glove." To have an extremely close relationship, especially at work.

Old hat

For example:

"I've been doing this job for so long it's all old hat now." Not new or different.

Burn a hole in one's pocket.

For example:

"He was never able to save any money, it always burned a hole in his pocket." To have money that you just want to spend.

Keep your shirt on.

For example:

"Stop shouting, keep your shirt on!" Don't lose your temper.

Lose one's shirt.

For example:

"He went to the races and lost his shirt." To lose all your money (usually in a business venture or by gambling).

In someone else's shoes.

For example:

"I hear he is very ill, I would hate to be in his shoes." To be in someone else's place or position.