The Exact Change Insister: 

Every time you buy something with cash, you must use exact change.  No matter how many people are behind you in line, you dig through your purse or pockets to find a dime and three pennies.  You dig for change like breaking a twenty is the end of the world.  It's not.  You create no value and waste everyone's time.

Here's an idea: Use paper money and let cashiers do their job.  They are usually very efficient and will finish the transaction quickly.  Whenever you get home, put your change in a bucket of some sort and take it to the bank when it's full.  This will save the world lots of time and frustration. 

Other annoying people.