Cross That Bridge When You Come to It. 

If you use a sledgehammer to crack a nut, you apply too much force to achieve a result. 

Crash A Party :

If you crash a party or are a gatecrasher, you go somewhere you haven’t been invited to. 

Cream of The Crop :

The cream of the crop is the best there is. 

Cream Rises to The Top :

A good person or idea cannot go unnoticed for long just as cream poured in coffee or tea eventually rises to the top. 

Creature Comforts :

The coziness of being at home

If a person said “I hate camping.  I do not like giving up my creature comforts,” the person would be referring in particular to the comfortable things he or she would have at home but not when camping. 

Crème De La Crème :

The crème de la crème is the very best of something. 

Crocodile Tears :

If someone cries crocodile tears, they pretend to be upset or affected by something

False display of grief

His cries were only crocodile tears.  Inwardly, he must have been happy. 

Crooked As A Dog’s Hind Leg :

Someone who is very dishonest is as crooked as a dog’s hind leg. 

Cross Swords :

When people cross swords, they argue or dispute.  This expression is used when some groups accuse each other for non-adherence to norms. 

Cross That Bridge When You Come to It. : 

If you will cross that bridge when you come to it, you will deal with a problem when it arises, but not until that point. 

Cross to Bear :

If someone has a cross to bear, they have a heavy burden of responsibility or a problem that they alone must cope with. 

Crossing The Rubicon :

When you are crossing the Rubicon, you are passing a point of no return.  After you do this thing, there is no way of turning around.  The only way left is forward.