Are there any situations in which it would be acceptable to say this to anyone?
Can "tråkig" mean sad as well? Or is it just a false cognate of the German word "traurig"?
No, but the adverb tråkigt can - e.g. Det var tråkigt = That's sad.
"Det var tråkigt." - That isn't an adverb though. It's an adjective in the ett-form! It means sad when describing situations and boring when describing people.
Yes, oops. I should have said e.g. tråkigt nog or similar. Must have had a brainfart.
It's idiomatic to say e.g. det var tråkigt to mean "that's sad", as in e.g. "I'm sorry to hear that". But the same phrase might mean "boring" as well. You can get around the ambiguity by e.g. saying vi hade tråkigt ("we were bored") instead.
Pronunciation: is the final "g" of "trakig" always missed, or is it a regional variation?