One-and-a-half Date
Not quite a double date, but not exactly a date either. It's when you invite someone out on a date, and they pull a defensive maneuver and bring a friend along, as a date shield.
Dude, I asked out that hot chick Sally on a date Saturday to cool party. She said yes, because she knew it was a cool scene, but she turned it into a one-and-a-half date, bringing along her BFF Tina to cock block.