Someone who breaks a pinky promise, on top of already being a jerk, hence being a doublejerk
You promised to run the mile with me! I don't feel well... Wow, Julie. You're a doublejerk!
Someone who breaks one or more pinky promises.
Ainsley: Julie, pinky promise you'll run the mile with me!
Julie: Okay! I pinky promise!
Ainsley: Hey, you never ran the mile with me! You doublejerk!