Living under a rock

If you are 'living under a rock,' it means that have not been paying very close attention to what's been happening (especially in the world) around you.

Example:
-I just can't comprehend how anyone could be an undecided voter at this point!
-They must be living under a rock!

Lost and Found

'Lost and Found' is a place where you can go to look for something you have lost, or to turn in something you have found. Usually restaurants, malls, hotels, parks, and the like, have a 'Lost and Found.' If you're looking for something, they'll often take your name and number so they can call you if it's found.

Example:
-Oh, no! I can't find my camera!
-Try Lost and Found. Maybe someone turned it in.

Lollygag

To 'lollygag' means to take your time when doing something -- not hurrying at all -- when someone has asked you to do something quickly.

Example:
-We're in a hurry, so please use the bathroom as quickly as possible.
-I know, Mom. No lollygagging!

Lying through your teeth

'Lying through your teeth' means you are completely and totally lying, probably in someone's face. It's stronger than just saying that someone is 'lying.'

Example:
-I stayed home last night, honest.
-You're lying through your teeth! I saw you at the bar last night!

Living under a rock

To say someone is 'living under a rock' means that they have not kept up with current events, trends or beliefs because they have kept themselves isolated or simply don't care. It is pejorative.

Example:
-Can you believe he still thinks it's okay to beat your children?
-What rock has he been living under?

Let's talk soon.

"Let's talk soon" actually means just the opposite. It's a way to end a conversation with someone, usually someone you haven't talked to or seen in a while, without appearing rude. When someone says this, they probably have no real intention of talking to you soon, and it could be a while before you hear from them again.

Example:
-It sure was nice seeing you again!
-It sure was! Let's talk soon!

Lay low

'Lay low' is what people tell you to do when you're sick, which means to rest and do as little as possible. However, this is a change-in-progress, because people lie and things lay. But it would sound quite odd to hear a native speaker of American English say, "Lie low."

Example:
-I feel awful. I have a fever, a stuffed up nose and a terrible cough.
-You'd better lay low for the next few days. Hope you feel better!

Let me let you go

'Let me let you go' is used in a phone conversation. The person who says it is trying to sound polite by saying they don't want to take up too much of the other person's time. The reality, though, is that usually the person who says this is simply trying to find a nice way to end the conversation without appearing rude.

Example:
-(slight pause in the conversation)
-Well, let me let you go. I'm sure you have a lot of things to get done today!