All for show

If something is 'all for show,' it means that something being done isn't genuine, but rather, it is being done to impress or to give a positive impression to someone else.

Example:
-I can't believe she got so emotional!
-Oh, that? It was all for show.

An accident waiting to happen.

'An accident waiting to happen' is how you describe a situation that is dangerous and could cause an accident. Everyone knows it's a dangerous situation, but usually no one does anything to fix it until an accident has already happened.

Example:
-They really need to get a lock on this pool gate. It's an accident waiting to happen!
-You're so right! I'll go tell the pool managers.

April Fool's Day

'April Fool's Day' always falls on April 1st and is a day of pranks and practical jokes. While it's mostly for kids, some adults also enjoy it.

Example:
-What's the best April Fool's joke you ever played?
-We got up really early and put salt in the sugar bowl. When our dad drank his coffee, he screamed and we laughed!

All tied up

If you're 'all tied up,' it means you're too busy to do whatever the other person is asking you to do. It's a typical expression you hear in an office.

Example:
-Can you go to lunch next Thursday?
-No, sorry. I'll be all tied up in court next week. How about the week after that?

All day

'All day,' as in "taking all day," or "I don't have all day" is a way to complain when you think something is taking too much time. It is usually said when the person being complained about is not within earshot, by a person who has power in a situation, or among close friends in informal situations.

Examples:

(To a friend while the salesperson in a store has stepped away) -What's taking all day?! It's just a simple return!

(To employees) -Come on, people! We don't have all day!

(To friends) -Come on, you guys! Let's go! I don't have all day!

Atkins

'Atkins' refers to a diet low in carbohydrates that can help a person lose weight. When Dr. Atkins first developed his diet in the 70s, the mainstream medical establishment was quick to dismiss him as a quack, as his beliefs flew in the face of conventional wisdom at the time. Today, after the failed low-fat diet fad of the 90s, which only made Americans fatter, low-carb diets in general and Atkins specifically are quite popular.

Example:
-Are you following any special diet to help you lose weight?
-Atkins.