pulling a shannyn

To commit to attending an event 100% and then not showing up. Especially if someone questions whether or not you will actually show up and you make a point of confirming you absolutely will attend.

"Hey wasn't Ben coming to the party tonight, I saw he RSVP'd and he told me he was coming?"

"Yeah, he said he was coming, but apparently he decided he was pulling a Shannyn instead"