As a Russian speaker, I would say that I feel our swear words become truly offensive when they are explicitly targeted at a person. "Dura" is also not considered to be an expletive, and I have not heard it being used in its original meaning after I finished 5th grade. Pronunciation in Russian is also different, word sounds like "doo-ra".

FWIW the same word "dura" may also be used as a slang word for a large and unwieldy inanimate object.