Today Is...International Day of Sign Languages

I once went to a Sign Language course at work and it began with the instructor telling us that he would teach us the most used words in the English Language so we could sign them, and then spent 10 minutes showing us as many swearwords as he could think of and the whole office spent the afternoon calling each other all sorts of names in sign language but apart from being able to tell someone to piss off (flicking the top of your index finger) i have sadly forgotten most but i do tend to fold my arms by putting the palm of my hands under my armpits which i found out means Crap so that's a bonus, unintentionally swearing to deaf people.
You don't need to go on a course to learn rude hand gestures because the British language has a rich source such as the V sign which is deemed the weaker cousin of the middle finger and mostly deployed by drivers when someone has cut them up.
Beloved by heavy metal fans, the horn sign may say you like headbanging but doing it at a Metallica concert in some countries in the Mediterranean and Latin America regions it means you enjoy watching your wife commit adultery with other men which could get your wife some unwanted attention.
If you want to order 5 of something you may push forward your hand with 5 fingers held up but do that in Greece and it's their version of the middle finger while if you do it in Iran you are suggesting that they drop dead which would probably end with you receiving 5 fingers curled into a fist and thrust forcibly onto your nose while in some African and Caribbean countries it means 'you have five fathers' thus calling someone a bastard which may see you not only not served but leaving the premises through a window.
I regularly use the Fonzy style thumbs up 'All Is Good' gesture but do that in some Arab countries and it's flipping them the finger but i am not one for the universal OK sign of making an O with your thumb and forefinger but if you are then you may want to just smile politely if you find yourself in the Mediterranean, Middle East and several South American countries where you are cheerfully calling them an arsehole.
In Vietnam if you want to wish someone good luck then crossing your fingers won't be particularly lucky for you because it depicts a woman’s genitalia, the hand-sign alternative of calling someone the c-word so doing what you think is universal sign language outside of your own land may seem a good idea but it might not be when travelling so keeping your hands firmly in your pockets may be your best option.