First, we have “air quotes”.

gestures air quote  

 “① is the sign to use when you say something really ironic.”

 “① is quotation marks, I think that what is said is meant to be in quotation marks. In English when words are enclosed in quotation marks it’s like using the phrase ‘so-called…’

People who use these are teased...a lot. Don't ever, EVER use these unless you're making a joke...

Number 2 doesn't have a name (and I can't find a good picture, but you see it a lot). You lick your finger and then touch someone's shoulder.

 “② is like “You’re hot!!!” in English an “On fire!!!” kind of comment.” But why spit?” Obviously the spit provides the reason to make the “pssss” sound that accompanies the gesture.

Number 3, when you “point fingers at your own eyes and then towards the other person", it means I’m watching you? or ‘watch your back.'”

gesture im watching you

This move can have a lot of variations depending on the hand movements and situations like “look at me” in reverse or “I see something over there” if pointing off to the side.

Number 4 is crossing your fingers behind your back, which means you are lying about whatever you are saying at that moment.

gestures fingers crossed behind back

Do you have a western gesture that you're unsure of? Ask me next time and I'll try to explain it to you!

Have a great day!