This question really shouldn’t be taking up so much space in my brain, but for whatever reason it still is, 24 hours later. So help me stop wondering about this, please.
I came upon the following passage in a book last night:
Now when I read this, I tried to picture it in my mind. And I just have no idea what the “cocksucker” hand gesture is, not to mention how it would involve a tongue.
Anyone care to educate me?
Isn’t that the one where you use your tongue to poke out your cheek, while simutaneously moving the fist in a horizontal motion. Like brushing your teeth, or something.
Hold your closed hand to your mouth like you’re holding a lollypop. Then stick your tongue in one of your cheeks. Move your hand toward your mouth like you’re giving a blow job and push your tongue in your cheek at the same time. The effect should look like a penis hitting your cheek and making it bulge out.
I watch too many teen comedies.
As Apricot mentioned, the “cocksucker” hand gesture I’m aware of goes like this:
(1) make a fist
(2) bring fist towards the mouth as though guiding a cock into the mouth, then pull the fist away from the mouth (a few inches). At the point where your fist is closest to your mouth, stick your tongue in your cheek to simulate a huge cock filling up your mouth.
(3) repeat continuously
Works best from the side. YMMV.
And that, children, is how you fight ignorance! 
Wow! Such fast resposes! Thanks guys, it’s very clear now.
Boy, Dopers do know everything.