Obscure Vocabulary Break!
What the heck is a “Tanas”? Well, as it happens, that’s the wrong question. The word does exist and it means a sort of useless, indecisive person, but “O tanas” is also an exclamation indicating disagreement or disbelief, so something like “That’s what you think” or “No way!”, or, of you’re in a hurry, “Bollocks!”
It seems to hardly appear online. Priberam defines it but Linguee doesn’t know about it at all, so I’d say probably not one to whip out in the supermarket.
Luso 
Porque não? Não aparece no Linguee porque a base de dados desta ferramenta é o português formal (não incluindo o literário) onde não se usa nunca frases deste tipo. É perfeitamente possível usar “o tanas” em discurso coloquial, informal (no supermercado). É, no entanto, antiquado.
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