In the almost fifty years I knew them, I never heard either of my parents swear. Ever. Not once. The worst thing I ever heard my mom say, when she pinched her fingers in the wringer washer once, was "Jezum Crow", and she apologized after. Nor did they use vulgarities, "barn words", and such. We were clean-talking.
Imagine my surprise after I became a Nazarene to find out that euphemisms for swearing (gosh darn it, gee, golly, heck, oh shoot, etc.) were, in many folks' opinion, just as bad because they were just a sneaky way of swearing and everybody knew what you meant anyway.
Our family's take on it was that use of the euphemisms was considered "anti-swearing". Saying "gosh darn it" was more or less a way of saying "I don't swear". Does that make sense? Ironically, many in the euphemisms-are-swearing crowd feel it's fine to say "Oh my" or "my goodness". Go figure.
I tried to find out from one man what was acceptable and what was not (wow? yikes? good grief? fiddlesticks? rats?) but I realized I was coming across as poking fun, so I let it drop. I never did find out the list of what's okay and what isn't.