The act of making a snake like sound when a fake-friend/scammer/snitch/two-faced/evil-person enters the room in hopes of reminding everyone else to watch what they say or else you could end up getting snaked in the future.
Matt: Yeah, I killed 5 of them mojitos last night and banged out two broads. what'd you do?
<Ray the Rapist enters the room>
Billy: It's snowing outside, how pretty.
Brittany: Let's go play in it.