You think someone is waving to you and, even though you don't recognize them, you wave back- just to realize they were waving at someone behind you and you're left flailing, trying to decide what to do with your hand to play off the fact that you just waved at a total stranger. Run it through your hair? Scratch a fake itch?
Once, during my Freshman year in college, I was on the receiving end of one of these awkward situations. The guy I was seeing and I decided to go on a very fancy date night to a high end restaurant. We dressed up, acted like we were adults who had class, and headed to the restaurant.. Once we were there, we fumbled over the menu, made a mess with the bread and butter, and didn't order booze out of fear of being pinned for under age and thrown out onto the street like a character in a predictable cartoon.
While we started to make our way through our sober, awkward, fancy dinner, the waiter came over with a bottle of wine. He leaned it against one arm so we could see the label and let us know it was from the gentleman at the bar. Confused, we turned toward the bar to find a man waving at us. Unsure, we both gave half smiles and waved back. As soon as we did this the man's face dropped. He rushed across the restaurant and stuttered out an apology. He thought we were someone else. Keep the wine. (Giving it back never occurred to me.) Sorry. Enjoy the wine, though. With deep crimson cheeks, he turned and quickly made his way back to the bar and avoided eye contact with us for the rest of the night.
That was awkward but at least we got wine out of it. Was it good? How the hell do I know? I was 19 and just trying to keep my bread crumbs under control.
(Not like I would know if it was good these days, either. And I'm still trying to keep my bread crumbs under control. Keeping it classy.)