Here are the keys to fighting off the triangle choke.
Posture up.
Go to knee up on the side of the trapped arm. Bring the other leg up tight under the guy's butt.
Grab the opposite collar as deeply as possible with the hand of the trapped arm and bring forearm across throat. In sparring, it can probably be across the upper chest.
Bring the up knee down around the leg and into the abdomen or lower chest.
Grab the pants by the butt with the hand of the free arm. That will help you turn in the direction of the trapped arm and the grinding knee.
Stack and grind from here, working around toward the trapped arm side and stacking--without standing. It's more of a low stack and grind. I'm going to call it the peppermill triangle defense!
