This one word in particular illustrates a whole panoply of inherently cultural terms - you might know them from the word anachronism. I pick sheepishly, or sheepish, not because it is something that I think you need to stop using, but because it is a perfect example of how real language works.
If you're crafting a world from scratch, or just using another culture, you can improve the realism of your world by altering and effecting the casual points of reference. You might notice that someone who lives in a world without sheep wouldn't say sheepishly, and just go with related terms like intimidated or meek instead. But that's not an accurate translation -- sheepish evokes a particular cultural narrative built on the stories we tell about sheep. Timidness, weakness, a general lack of bravery and will, all based around the animal we know, and stories related about them.
When you're writing your novel, do you take care to check your points of reference? Do they fit the locale, the culture of the people you're writing?
Here's a particular fun fact not everyone knows: In Quebecois, normal curses are parts of churches or other references to Catholicism. One of my favorites is Tabernacle, which is pronounced Ta-bar-nak. It's the same basically as saying shit or fuck as an ejective curse.
Creating or adapting local cultural references will make your story more believable and offer a convenient way to censor your book, as censors don't identify cursing by syntactic position. It's really just a list. Outside of the seven dirty words, you can curse your way to kingdom come and maintain a PG rating. Or, in the case of Battlestar Galactica, just get to say an F word that wasn't fudge.
I'm not advocating for the disuse of fuck and shit, and other dirty words, (though I do wish writers would choose a wider variety of words for penises than "cocks." No one seems to want to call them penises in sexy scenes. It's only cocks. And that word really gives me a whole assholey vibe. Not sexy either.) my original world fantasy includes fuck and shit when appropriate. But you should look for opportunities to worldbuild a little when it comes to points of reference and curses. Sure, your people might have one God same as many in the real world, but is it the same one? What's your God's name? Is it something that gives you a vibe for who that god is, and what they stand for? Is it something you can make interesting curses with?
As example, in my current major WIP there are a group of people who worship the Ancients, the mythical ancestors of all people as gods. In their culture, they believe the Ancients ascended to a massive superstructure that circles the planet called the Ring, and that if they are faithful enough, they will go up too.
So instead of "My God!" It's "Ancients above!" There are others as well, that help give some historical perspective, hints to the past and the truth of the world. "Nine stars not fallen!" a curse for a serious occasion, gives you a clue as to why the sky described in my world has very few stars (nine to be exact, hurr hurr). Given the proper context and background, made up curses can provide an equal, if not greater power of invective than natural curses.
For those writing our-world fiction, you're obviously going to appropriate real world references. But the lesson of modifying your narration to match the time and place is applicable to all. If you're from Brooklyn and you're writing a story set in France, you probably wouldn't (unless it was to hilarious effect) have your characters and narration use Brooklyn slang and references. And vice versa.
So read through yours - does your narration and language reflect the world you are using? If not, do your characters recognize the anachronisms, or is it something you just ignore?