Some years back (okay, back in the Eighties) I camped in Scotland at a place called “Faichemard Farm” (that’s “ch” as in “loch”). “Faichemard” is Gaelic for “high pasture” or something like it, but it does duty very nicely as an interjection. 
Dad always said “Dillywiggers!” Taught it to my kids as a swear word, and they would try to use it to shock me. What fun.
What about “mung”?
Thanks to Rex Stout, I’ve always been fond of “Pfui” myself.
I’m very fond of Terry Pratchett’s using of ----ing ----ers (the dashes are pronounced) in Thief of Time.
Belgium
You knew this one was coming…
Crip. Sorta like crap. That’s my new swear word. It’s me trying to clean up my language in front of my 12 y.o.
A former English Comp teacher used to bark out “Bolshevik!”
I adopted it.
I guess I’m really Old School [sup]tm[/sup], because MUNG is a recursive acronym, meaning Mung Until No Good.
A running gag on the Snopes message board is replacing swears with “NFBSK,” short for “Not for British school kids.” I don’t know how this would be pronounced. And of course, there are the various Fark swear-replacements- “fark,” “shiat,” “cvnt,” etc.
Well then, my boy! You’ve got a bit of Googlin’ to do!
“Criminently” (derived from “criminy,” in turn derived from who knows what) is supposedly an old standby for kids whose parents wouldn’t let them swear.