"Gosh-darn" is a mildly derogatory expression that is used to express frustration or annoyance. However, if you are looking for alternative words to replace it with, there are plenty of other synonyms that you can use. Some good examples include "blast," "darn," "dag-nab," "heck," "drat," "rats," "cripes," and "gee-whiz." Each of these expressions carries a similar connotation to "gosh-darn," although some are more mild than others. Ultimately, the choice of which synonym to use will depend on the situation and your personal style of speech.