Here is our list of American idioms that start with "P":

Pack heat; to be packing: To carry a gun.

(A) pain in the butt:
A problematic person/thing; a chronic complainer. Examples: "I hate doing my taxes. It's such a pain in the butt."; "Stop being such a pain in the butt. All you do is complain!"

(To) pass the buck:
To blame someone else. Example: "It's much easier to pass the buck than to take responsibility for something."

(To) pass the time:
To do something to keep busy. Example: "What do you do to pass the time around here?"

(A) pat on the back:
A sign of approval; "To give someone a pat on the back" means to show them that you approve of something that they did.

(To) pay an arm and a leg/ pay a fortune:
To pay a lot of money. Example: "I hate to have to pay an arm and a leg for a pair of tennis shoes."

(A) peeping Tom
Someone who looks through people's windows. Example: "Larry was a peeping Tom. The neighbors caught him looking into Sarah's window one night."

Peppy (adj.): Energetic, lively. Example: "A peppy song"

Pick back up: To start again. Example: "Let's pick back up where we left off."

(To) pick up the tab:
To pay a bill. Example: "John, you picked up the tab last time. Let me pay this time."

(A) piece of cake:
Very easy. Example: "P1: Hey how did you do on the test? P2: I aced it. It was a piece of cake for me."

(To give someone) a piece of one's mind:
To scold, reprimand someone (for something they did). Example: "After I found out how badly Peter had treated his girlfriend, I gave him a piece of my mind."

(To) pitch in:
To help with something (especially financially). Example: "Let's all pitch in and buy him a nice present."

Plastered (adj.):
Very drunk. Example: "I got plastered last night."

Plead the fifth (v.):
To be able to answer a question, but to choose not to. Example: "P1: Did you see my husband at the bar? P2: I'm gonna plead the fifth on that one. I'd rather not get involved."

(To) play second fiddle to someone:
To be second in importance to someone. Example: "Sam didn't join the team because they already had a star and Sam didn't wanted to play second fiddle to anyone."

(To) play something by ear:
To improvise. To see how things go and make a decision later. Example: "P1: What do you want to do tonight? P2: I don't know, let's just play it by ear."

(To) play it safe:
To act or be safe. To do something safely. Example: "Sarah isn't much of a risk taker. She likes to play it safe."

(To) play the field:
*somewhat outdated* To date many different people instead of going steady. Example: "After Mary broke up with Jim, she started playing the field."

(A) poker face:
A face with no expression. Also common is "to be poker-faced."

Preachy (adj):
An adjective that describes someone (or something) that tries to preach how one should live, etc. Example: "A preachy movie"

Pressed for time:
In a hurry. Example: "I'd love to stay and chat, but I'm a little pressed for time."

(To) promise someone the moon:
To promise someone lots of extravagant things (unrealistically). Example: "He promised her the moon, but couldn't deliver on any of his promises."

Psyched (adj.): Excited. Example: "I'm so psyched about the concert tomorrow!"

Psycho (n.): Crazy, mentally-unbalanced person. Example: "You should stay away from him. He's a bit of a psycho."

(To) puke:
To vomit. To throw up.

(To) pull someone's leg:
To kid, play a joke on someone. Example: "When he told me he was joining the military, was he just pulling my leg?"

(To) pull a fast one:
To cheat or to deceive. Example: "Con men are experts at pulling a fast one on unsuspecting passers by."

Pure gold:
* somewhat outdated* If something is "pure gold" it is "the best", "fantastic", "amazing".

(To) push one's luck:
To expect continued good fortune. Example: "Don't push your luck. I was nice to you before, but if you keep making me angry, you'll regret it."

Put someone through (a lot)(v.): To make someone suffer (a lot) Example: "After all he's put her through, I can't believe she still loves him!"

Put the moves on (someone)(v.): To hit on (someone), to try to seduce (someone). Example: "Was he putting the moves on you?"

(To) put up a good fight:
To try very hard. Example: "Well, although my team lost, they put up a good fight, so I'm not upset."