You keep using that word... I do not think it means what you think it means..
Du fortsetter å brukke det ordet ... jeg tror ikke at det betyr hva du mener det betyr.
(Just testing to see if there are any corrections that might make it sound more natural in Norwegian. :-) )
Can it also mean unbelievable in a negative way?
Probably, but it would likely be "Så utrolig da!" if you wanted to be sarcastic.
I understand that Så is so but what is da?
Da usually means then, but it is in frequent use as a filler word... not meaning much. It would be strange to translate it to then in this context anyhow. Or could you say things like "how about it then?" where then doesn't really carry a meaning?
Yeah when I heared it while I was watching NRK I thought it was "det" but it wouldn't make sense, tusen takk.
Why not extraordinary?
Yes, you're right. "Extraordinary!" can be used both to express wonderment as well as incredulity. I've just added it. :0)