Trás-trás
Trás-Trás is a peculiar movement done by some drunk people in the Lisbon night.
You can catch some of them doing it in the famous disco Kapital.
Is it a dance movement ? No.
What does it mean ? Not even the ones who do it know it.
Nowadays there's a variant, "Trás-Trás dinâmico" (Dynamic Trás-Trás), with two main differences: thumb and middle finger of the left hand point to the left and the right, while the one doing it does a kind of ugly face, reminding a pig.
Also nowadays, the move is expanding little by little throughout Portugal.