Cursing and cussin'.

I've shared here the story before of a friend who said having a child turned her into Yosemite Sam, because she had to replace all her naughty language with G-rated or at worst PG-rated words. 

The patron saint of swearing
without actually cursing

We generally know that most such mild appellations are euphemisms because of their similarity to the actual naughty words -- as George Carlin pointed out, shoot is just shit with two O's. Shucks goes all the way back to 1847, and is used the same way. See also sugar, which I think is a more recent interjection invention.

Some cuss words that we think of as pretty mild, however, are even worse than the ones we actually use. Some are straight-up blasphemy, like zounds! (short for "God's wounds!" meaning the injuries of Christ's Passion and death) and odds bodkins! (which was "God's body!"). The British blimey! is the shocking expression "God blind me!" to express shock, and egad! is the milder "oh, God!"

To get more into Yosemite Sam territory, we have the swear word drat!, which is the kind of thing that would get you laughed out of the biker bar. But drat is thought to be a contraction of God rot -- in other words, hoping that the person would be divinely condemned to rot, likely in hell. Thus, the Snidley Whiplash "Drat you!" is even worse than an effenheimer. Consarn's origins are a little fuzzier, but are considered to be connected to damn, and thus another hope that the hearer would be sentenced to eternity in hell. Compared to that, telling someone to perform an impossible biological function on one's self, while likely painful, would only be of temporal disquiet. Dadgum is also a spoonerism for God damn -- think of that next time the kids make you watch Cars. That Mater is one foul-mouthed tow truck. See also gosh darn, gul durn, gul dang, etc.

It's kind of funny how we went from thinking that the wrath of God was less of a curse than telling someone to, say, doody in his hat, but there we are. (Doody, by the way, as a euphemism for, well, poop, is also of mysterious origin, which is probably not much consolation to the many fine Doodys of County Mayo in Ireland.) When Deadwood was running on HBO, I read that while the idea of bad language was captured by the show, the actual Western bad language would have been more blasphemy, less biology. But I never saw the show, so I can't confirm. 

I could go on with this doody all day, but I leave you with this amusing list from The Tennessean of fifty swear-word replacements for when you're trying to keep it family-friendly. My favorites on the list, which I will undoubtedly use, are: 

William Shatner!

Frack!

Zoinks! 

However, they did put a few on that list that also have blasphemous origins, like gadzooks! ("God's hooks," as in what He hung on on the cross) and crikey! (a euphemism for "Christ"), as well as blimey! You just have to hope the toddlers around you don't have an Old English Dictionary available.