Admit it. You’ve been stumped by apostrophes before. There’s no shame in it — even for word-savvy types who know all too well the difference between “lets” and “let’s” and who can spot a misplaced apostrophe in “Welcome to the Smith’s house” from a mile away.

Apostrophes are used in many situations — too many, really — ranging from the super-easy “the dog’s tail” to the super-arcane “attorneys general’s.”

This week, let’s look at the far end of the difficulty spectrum: The apostrophe uses that can stump even the very best of punctuators. Here are some of the toughest situations for knowing when to pull out an apostrophe.

Do’s and don’ts

The most important rule of using apostrophes well is: Never use an apostrophe to form a plural. It’s two luaus, not two luau’s. The expression “do’s and don’ts” flies in the face of that rule. “Do,” theoretically, should take “dos” as its plural. And it can, according to Merriam-Webster, which allows either “dos” or “do’s.” But in Associated Press editing style, the “do’s” have it. So you can write “dos and don’ts” if you like, but “do’s and don’ts” is more standard.

Attorneys general’s

You may know that, the plural of “attorney general” gets the S at the end of the first word: Attorneys general. But once you’ve made it plural, how do you make it possessive? You put the apostrophe and S at the end of “general,” not “attorneys.” When multiple attorneys general hand down a decision, it’s the attorneys general’s decision.

Mother’s Day, Father’s Day, Presidents Day, Veterans Day

My advice: Don’t bother trying to memorize which holidays have apostrophes. The rules aren’t logical. For example, Mother’s Day honors many mothers. But the name suggests a singular Mother. Presidents Day is correct without an apostrophe in AP style but takes an apostrophe after the S in Chicago editing style: Presidents’ Day. Yet both these influential styles agree there’s no apostrophe in Veterans Day. Fortunately, they’re all in your dictionary. When you need to get one right, just look it up.

Single quotation mark instead of apostrophe in ’80s

Your computer is out to get you. When you type an apostrophe at the beginning of a word or number, it assumes you wanted a single quotation mark. The single quote mark curves with its opening to the right, like the letter C. The apostrophe curves the other way, like a backwards C. To fix this, type the apostrophe twice then delete the first one. And note there’s no apostrophe before the S. Numbers and decades like ’80s and 1900s don’t take an apostrophe before the S.

Goodness’ sake, conscience’ sake, appearance’ sake

The Associated Press Stylebook has rules for “sake” expressions, but they’re style rules, not grammar rules. That means you can ignore them if you want. But when you just want to be sure you’re not making an embarrassing error, AP is as good a guide as any. It says that when a word that ends in an S sound (not an S necessarily, but an S sound) and is followed by an S, you drop the extra S you would have used to make the possessive. That’s why “appearance’ sake” and “conscience’ sake” and “goodness’ sake” have no S after the apostrophe.

Kids’ and children’s

Kids and children are plural synonyms. But “kid” forms its plural the old-fashioned way by adding an S at the end, while “child” is an irregular noun with the plural “children.” The rule for making plural nouns possessive is: Put an apostrophe after the S for a regular plural: Kids’. But for an irregular plural that doesn’t end in an S, put an apostrophe plus an S: Children’s.

Todd and Jane’s house, Todd’s and Jane’s cars

When you’re talking about multiple people owning things, here’s the rule: If they share the thing, they share a single apostrophe and S: Todd and Jane’s house. But if each has his own thing, like Todd’s Honda and Jane’s Ford, each gets his own apostrophe: Todd’s and Jane’s cars.

A’s and Bs and c’s and d’s

That rule that says to never use an apostrophe to form a plural — well, sometimes it doesn’t work out too well, like when the S forms a new word, “as,” or when writing about individual letters, like C, in the lowercase. In these situations, the rules are made to be broken.