Pistol

A 'pistol' is a type of handgun, but it can also be used, especially by grandparents, to describe a small child who is very cute or doing something sweet or ornery.

Example:
-C'mere, you little pistol! Nana loves you!
-Love you, Nana!

Under the gun

If you're 'under the gun,' it means you're under a great deal of pressure to get something finished and there's not much time left.

Example:
-Hi, Elizabeth. So, how is your sister doing?
-I'm sorry, I really can't talk right now. I'm under the gun. My presentation has to be ready in an hour.