Monetary pet peeves (in no particular order):

By United States Mint - http://www.usmint.gov/pressroom/index.cfm?flash=no&action=photo#Pres, Public Domain, https://commons.wikimedia.org/w/index.php?curid=31105133

1: Pennies. I am a strong believer in the idea that the penny should be discontinued. They are a waste of money, for a variety of reasons:
1. At last report, it costs 1.7 cents to make a penny (I keep finding numbers between 1.5 and 1.8 cents, but 1.7 is the most common that I can find). For every dollar we spend to make a penny, we get less than 59 cents worth of currency. That is throwing money out the window.
2. Finding exact with pennies is a waste of time. Federal minimum wage is currently $7.25, which is about 0.2cents/second. Every minute that we spend fiddling with messing with pennies or waiting for people who are fiddling with exact change is another 12 cents lost.
3. People actually throw pennies away. As in, vacuum them up while cleaning, toss them in the garbage while emptying pockets, and the like, forcing garbage companies to have to sort the change out from the rest of the trash.
4. Many cash machines do not take pennies. I know for a fact that the self-checkout at the grocer by my place takes pennies, as do the city buses and the coin things at the banks. That's pretty much it. Granted, I don't live everywhere, so your milage may vary with what actually takes pennies.

 

By United States Mint - United States Mint Image Library, Public Domain, https://commons.wikimedia.org/w/index.php?curid=46235336

2: Dollar bills. It's time to fully switch over to the $1 coin full-time, and replace the $1 bill with the $2 bill. Or better yet, also bring in the $2 coin. It costs 5.5 cents per note to make each $1 and $2 bills, but the $1 bill has an average lifespan of 2-4 years. Though it costs about 18 cents to make a dollar coin, coins have a lifespan of closer to 35 years. In short, we can have a coin that will last a whole generation that will cost us 18 cents, or we can spend about $48 to keep making a new bill over and again to replace a destroyed one in the same amount of time.

 

By Edward M. Weeks, Bureau of Engraving and Printing - Extracted from PDF version of Commemorating the Seal poster, part of a State Department exhibition on the Great Seal. Direct PDF URL [1] (33MB), Public Domain, https://commons.wikimedia.org/w/index.php?curid=5313214

3: "In God We Trust" needs to be removed from our currency - in fact, it should not be the national motto. E pluribus unum, "out of many, one," is a much better motto, for it better reflects the infinite diversity that is found in the great mosaic of American society. Also, we are a nation that has separation of church and state. We should not be promoting a religion as the power of the nation, but rather promote the unity that brings us all together.
Aside from my belief that it is a violation of the first amendment, my reading of various christian doctrines suggest that having this on our money is a violation of those doctrines. Specifically, Exodus 20:3-6, Deuteronomy 5:7-10, Exodus 32, Mark 12:17, and all the times that Jesus whipped moneychangers. I don't know about other religions, as I have not researched as deeply into money worship. But I do know that even President Theodore Roosevelt found having "In God We Trust" on our money to be sacrilegious.
Anyway, out money didn't always have "In God We Trust" on it. But there is a long history where we kept putting it on more and more things. And here we are now.

 

4: When people and machines don't have their money all facing in the same direction. I'm kind of a curmudgeon that way, I'll admit - I developed the habit when I was first working retail and had to repeatedly count stacks of money, and then wait at the bank for the bankers to count the money. But I find that the money is easier to count when it is all facing the same way, anyway.

 

Read More:

CGP Grey:
"Death to Pennies" http://www.cgpgrey.com/blog/death-to-pennies.html
"Canada Gets Rid of the Penny" http://www.cgpgrey.com/blog/canada-gets-rid-of-the-penny-huzzah.html

VlogBrothers:
"I HATE PENNIES!!!! (Also Nickels.)" https://youtu.be/77C47XYm_3c
"Kill the Dollar Bill!" https://youtu.be/SHC2pqxdjlQ

Last Week Tonight with John Oliver:
"Pennies" https://youtu.be/_tyszHg96KI

 

References:

United States Government Accountability Office Report to Congressional Requesters, December 2015: http://gao.gov/assets/680/674120.pdf

CNN Money "Pennies and nickels cost more to make than they're worth" Jan 11, 2016: http://money.cnn.com/2016/01/11/news/economy/u-s-coins/

CNN Money "Should the U.S. kill the penny?" Feb 4, 2013: http://money.cnn.com/2013/02/04/news/economy/end-of-penny/index.html?iid=EL

Time "The Government Lost Money on Every Penny It Made in 2016" Dec 27, 2016: http://time.com/money/4618271/penny-cost-make-worth/

Wake Forest University "Professor's research supports eliminating penny" July 18, 2006: http://www.wfu.edu/wfunews/2006/2006.07.18.w.html

CBS News "Americans throw away $62 million in coins each year" Oct 18, 2016: http://www.cbsnews.com/news/americans-throw-away-62-million-in-coins-each-year/

US Federal Reserve: https://www.federalreserve.gov/faqs/currency_12771.htm

Dollar Coin Alliance: http://www.dollarcoinalliance.org/facts-about-the-dollar-coin/

New York Times "ROOSEVELT DROPPED 'IN GOD WE TRUST'; President Says Such a Motto on Coin Is Irreverence, Close to Sacrilege. NO LAW COMMANDS ITS USE He Trusts Congress Will Not Direct Him to Replace the Exalted Phrase That Invited Constant Levity." Nov 14, 1907: http://query.nytimes.com/gst/abstract.html?res=9406E2D8103EE033A25757C1A9679D946697D6CF&legacy=true

US Department of the Treasury "History of 'In God We Trust':" https://www.treasury.gov/about/education/Pages/in-god-we-trust.aspx