Darnation is a euphemistic term that is used to express surprise, frustration or annoyance. However, if you're looking for synonyms for this word, you can try using other similar phrases such as darn, blast, drat, gadzooks, bugger, or confound. Additionally, you can use more subtle terms like goodness, gracious, heavens, or gosh to replace darnation in your speech or writing. These synonyms convey similar emotions and sentiments while steering clear of offensive language. Remember that it's important to choose your words wisely depending on your audience or situation.