Ork (of Mork): Shazzbat!
Klingon: several, see here. My favorite is “HuH”. Huh?
What else?
My favorite fictional curse is from the Pirates of Darkwater cartoon (not really alien, I know).
Noy Jitat!
Farscape had some, such as frell (and variations).
The original Battlestar Galactica had “felgerkarb.”
“Belgium” from the Hitchhiker’s Guide books
“Frack” (as a substitute for fuck) from the newer version of Battlestar Galactica…which kinda adds some unintentional humor to news stories about fracking in the oil industry.
Belgium!
Swut
Ju-juj flop
Turlingdrome
All from The Hitchhikers Guide to the Galaxy (radio version at least)
DC comics’ Interlac has ‘sprock’, ‘nass’ and ‘grife’.
From the Mass Effect series, Quarian “bosh’tet!”
The Orions in the Starfire series have Chofak: The literal meaning is “eater of midden scrapings,” though generally translated as “dirt eater.” It is used to mean someone so lost to honor as to have no true conception of it.
Book version, too.
Larry Niven’s carnivorous kzinti use “leafeater” as an insult. Not quite the same as a swear word, but close.
Not an alien curse but “tanj” was used as an expletive in his Known Space books.
(There Ain’t No Justice)
From Alien Nation, “ss’ai k’ss”, two words which mean “excrement” and “cranium”. Colloquially, “shithead”.
The Coneheads would sometimes swear by saying “Mebs.”
Frack was also used in the original series.
Also, “censored” was used as a cuss word.
I read a fantasy series a long time ago, and don’t remember much about it, other than dwarves used “rust” as an expletive.
I’m willing to be that “motherfracker” wasn’t, though.
Farscape had a huge number of swear words…
Frell, Dren, Drannit, Hezmana, Greebol, Loomas, Fahrbot, Tralk, Mivonks, Frelnik, Thoddo and Yotz
My current favourite is in Guardians of the Galaxy comics, where they say D’ast.
Mine too! "Jitatin’ " as well. And definitely alien - Mer’s not Earth and its inhabitants are only humanoid.