Murphy Duck

The act of leaving a bar, restaurant, or other social gathering, usually serving alcohol, without informing your friends or party in advance, or only sharing the information with a select one/few before your departure. Chicago Southside in origin.

"Hey, anyone see Mick?"
"Ahh, the bastard musta pulled the Murphy Duck..."

"FFS... My ex just showed up. I'm gonna pull a Murphy Duck out the back before she sees me. Later..."