Someone I know says "Oh for crying in the beer!" instead of "oh FFS", and calls people a crothound or an idiot prune instead of anything actually sweary when they do something stupid. She says it gets their attention better. You can invent your own, though you'd need to consult Urban Dictionary to make sure nobody is using that particular word to mean (say) testicles this week.
My favourite, to someone who carved her while she was driving, went, "You jumped up, never come down, blind, blithering, half-baked, size twelve ego in a size five soul." It made us both laugh and she felt better too.
Slack-twisted is good. Oh, there are oodles of words which sound awful and don't mean anything particularly bad.... I mean, mawkish? Gruntfuttock? Splot? Spurge? Martlet?
Or there is using something which has a meaning everyone knows but which is irrelevant: "you perishing bicycle chain!"
After a bit a mere unimaginative fuck or bugger sounds terribly mundane and boring.