Should adjectives that refer to people or cities be capitalized? "Live a Spartan life" "Life is Roman in its opulence."?

I’m writing some calendar photo captions and I’m making a joke about the Ides of March, with references to Spartan and Roman. I think these are simple adjectives and should be lower case. May I capitalize the words just to draw attention to the joke, or would the people who get the wordplay just be annoyed that I wrongly capitalized the words?