Stuff like “god damn”, “fucking hell”, etc. Anything that stems from religious sources. That includes fudged varieties like “jeez/geez” and “heck”.
And to clarify, this isn’t some attempt to avoid blasphemy or anything. I’m not particularly religious and would rather rewrite the neural pathways for those “defaults”, but haven’t been able to come up with satisfactory alternatives so far.
*To clarify further, I’m all good with most other curses (shit, fuck, ass, etc). I’m not trying to be inoffensive, just non-religious.
I like the in-universe swears from some of Brandon Sanderson’s fantasy novels: Rust (rusting, rusted) and storms (storming) come to mind.
A québecoise roommate of mine got her whole office yelling “chicken FRITE” (fried chicken in franglais).
“What the shoes” is kind a fun one. I’ll also yell “fudge knuckles!” which doesn’t really mean anything but is pretty satisfying to say.
The Wheel of Time has some great ones too.
Blood and bloody ashes
Mother’s milk in a cup
Son of a goat’s left stone.
See also: Battlestar Galactica
Oh and Firefly, although a lot of that is in Mandarin.