In my e-book, I mention that apostrophes make words possessive or appear in contractions for the missing letters. That means the following words, even if they look incorrect, are actually correct:
- dos and don’ts
- ifs and buts
- yeses and nos
- And yes, even those terrifying ROUSes
The only exception I can find is making one lower case letter a plural, such as “mind your p’s and q’s” (The Chicago Manual of Style, 7.14).