To be the bee's knees
If you think something is the bee's knees then you think it is the best, or really good quality. You could also say "She thinks she's the bee's knees" which means that you think someone is arrogant or self-centred.
The pot calling the kettle black
"That's the pot calling the kettle black" is a phrase you can use if you hear someone criticising someone else when they are not perfect themselves. It could be a gentle warning that we are not all perfect!
To keep your eyes peeled
Sounds painful! But if you ask someone to keep their eyes peeled, you are asking them to look carefully for something.
To pull someone's leg
If you tease someone, or try to trick them by telling a little lie, then you are pulling someone's leg. It's always meant in friendly way. If you don't believe what someone has told you, you can also ask: "Are you pulling my leg?" to show that you don't believe them.
To have kittens
To have kittens is an expression used when you have a sudden surprise which makes you feel worried, anxious or slightly fearful. "I nearly had kittens when I realised I'd left my passport at home"
To give someone the hairdryer treatment
Made famous by Sir Alex Ferguson when he was manager of Manchester United. If he was angry with his players, he would give them the hairdryer treatment at half-time - that is to say, he would shout at them very loudly, very close to their faces, to express his anger.
To have your finger in too many pies
If you have your finger in too many pies, you are involved in too many projects at the same time, and as a result you are not doing any of them very well.
If you are caught red-handed, you have been found in the act of committing a crime! It probably comes from the idea of criminals being found with blood on their hands, before they had time to clean it off.
To chicken out
Poor little chicken! To chicken out of something means to decide not to do something because you are afraid.
To catch (or have) forty winks
Nothing to do with a twitching eye! If you catch forty winks it means you are having a nap, a snooze, or a very short sleep, often during the day.
The green-eyed monster
This is a way of describing jealousy or envy. You can also say you are 'green with envy'.