When we talk, we use more than just words. We also do gestures that can be as meaningful as the words we say. Some of them are universal (such us “thumbs up”), some others mean different things in different places.
People from Buenos Aires are known for “speaking with their hands”. You might feel that we  are making senseless chaotic movements but many of them are  very meaningful and clear among locals.
Here, some of them.

¡Ojo! – Be careful!/Watch out!

[Pull down your lower eyelid with your index finger.]

¡Ni la más pálida idea! – I don’t know./I have no clue.

[The chin flick: tilt your head back a bit and sweep the back of your fingers forward from under your chin.]

¡Ma sí, andá (a cagar)! – Get outta here!/ F*ck off!

[Throw your arm back toward your head.]

Montoncito – What the hell are you talking about?!/Just who do you think you are? 

[Bring all of your fingers and your thumb together with your hand pointing upward. Move  your hand up and down at the wrist.]

¡Hambre! – You’re totally in the dark, out of it. You don’t know what time it is. 

[Bite your lower lip with your upper teeth and say: “mmmh!”]