Start with a seated (butterfly) guard, at a very short arm's reach from your partner. With your right hand, reach for their cross collar, but don't grab anywhere near as deep as you might for an X-choke. Instead, shoot for your knuckles to connect with their collarbone. This is far less likely to alert your partner to the impending dangers than an ultra-deep feed.

The best time to make this initial grip is when your partner happens to be looking down; this will facilitate the completion of the choke as well. With your free (left) hand, push your partner's head down, while lifting your right elbow. Without releasing the pressure that's pushing your partner's head downward, shoot your left hand through your own elbow, and flare your fingers out, creating a hook of sorts (with your right forearm). Push straight downward to get the choking finish (you can also turn to your left, but this will facilitate a sweep, offering your partner an easy way out from the submission).