Come hell or high water.
No matter what (I will do this or that no matter what / This or that will happen no matter what).
A dime a dozen.
Something that is very common / very easily found or acquired.
Get out of hand.
A situation can "get out of hand" = get out of control.
To add insult to injury.
To make matters worse.
Don't count your chickens before they hatch.
Don't count on something good happening until it's happened.
You can't swing a dead cat in here without hitting someone you know.
Beat around the bush.
Being very vague on a subject or a matter.
To pull someone's leg.
To joke with someone.
To be barking up the wrong tree.
To be mistaken / To be looking for solutions in the wrong place.
Don't give up your day job.
You're not very good at this.
I intend to be very frank.
I will tell you exactly what I think about this and that (without sparing your feelings on the matter).
Bite the bullet.
Doing something that you really do not want to do, but that you have to.
To get bend out of shape.
To get very irritated or annoyed in a counterproductive way.
Birds of a feather flock together.
People who are alike are often friends (usually used negatively).
Go on a wild goose chase.
To do something pointless.
When push comes to shove.
When things escalate quickly to make the situation worse/more serious.
Break a leg.
Good luck.
Under the weather (/I am feeling "under the weather").
To be ill.
By the skin of your teeth.
Just barely.
He has bigger fish to fry.
He has bigger things to take care of than what we are talking about now.
All of a sudden.
Out of the blue / suddenly / without warning.
Cut me some slack.
Don't go to hard on me. Don't set your expectations too high.
We'll cross that bridge when we come to it.
We will deal with a certain problem that we have anticipated, later when it becomes relevant.
Comparing apples to oranges.
Comparing two things that cannot be compared.
He's a chip off the old block.
The son is like the father.