A basic yet popular writing question is should nicknames be capitalized? This is one made more complex than it should be. Yes, nicknames should always be capitalized.
This does not only go for people either. It also goes for nicknames of places and things as well.
Why Should Nicknames Be Capitalized?
As an author, you like to be thorough with your novel. You are going to need more assurance than a simple yes.
The reason nicknames should be capitalized is they are proper nouns. If they are being used instead of the character’s name they should certainly be capitalized. Once again this also applies to the nicknames given to places and things.
If you can directly substitute the character’s name for their nickname in the sentence, capitalize the nickname. There is no reason to overthink it.
What About Insulting Nicknames
Insults can be a bit more complicated, but they are still quite simple. If your character is being called an insult as their name, capitalize it. A good example of this is Shithead. You can substitute your character’s name for Shithead, even if it is a generic nickname.
This is different from someone calling someone an asshole. In that case, you would not substitute the character’s name for asshole, so it remains lowercase.
Again this also applies to places and things. In general, if the original name can be substituted for a nickname, the nickname is a proper noun and should be capitalized.
Should You Capitalize Terms of Endearment?
When you use any term of endearment, it should not be capitalized. This is because it is not a nickname and can not quite be substituted for a name in all situations. It may work sometimes, but not consistently.
For example, your character’s wife may call them sweetie. However, you are unable to substitute their name if the wife is talking about your character. They would not then go to their kid and say “Sweetie went to work.” Therefore it is lowercase.
Obviously, if there is a dog named Sweetie this is a different story.
To summarize, nicknames are always capitalized. Terms of endearment are not nicknames.
If you use a nickname for anything, anyplace, or anyone in your writing capitalize it. Do not overthink it. If you get stuck, check that you can substitute the actual name for the nickname. If so, it is a proper noun. Proper nouns should always be capitalized.