It's a direct and often vulgar term, used casually in that era. However, it's important to note that language evolves, and the specific connotations of words like "tang" can shift over time.
If you're interested in exploring the evolution of slang and its use in specific periods, consider looking into dictionaries of slang from the 1970s or researching online resources like the Urban Dictionary, which documents the changing meanings of words and phrases.