On the second episode of Friends, "The One with the Thumb", Phoebe is giving an old lady a lot of money. While she's doing this, watch the sidewalk, a guy is walking down the road, looks directly at the camera, and waves!
Lizzie, the old lady that Phoebe gives the money to, is sitting next to a entrance to the subway. The guy you see waving is waving to someone coming out of the subway. You pretty much only see his head, and, only for a second, there's clearly someone there that the guy is waving to.