Faen - derived from 'fanden' = the devil/evil one - but today; used kinda like fuck Helvete = Hell Herre gud = O my god (not really cursing) Dust = Idiot, also used for Jerk Fehue = literary 'Sheepshead' could also be used as Idiot Hurpe = Bitch (the curse not the female dog) Jævel - derived from djevel = devil/demon
I deliberately did not include curse words involving genitalia. If you want some, just let me now. A bit of context is also useful... Is he trying to insult someone, just reliving some anger or cursing and inanimate object?
As for "Off worlders" ; No good term for it. Directly it would be "Av planetere" but that just wrong. It could be translated as "Fra en annen planet" or "Ikke fra denne planeten". "From another world", "Not from this world" respectively. Could use 'utenforstående' = outsiders, but it sounds kinda formal... Let me think about it.