A few years back, during a very smooth Atlantic crossing, someone (never did find out his callsign) on the chat frequency was asking for ride reports at 36000' having just passed 30W. All the responses were "smooth ride" all the way across. One American pilot, who it would seem had worked out that he was two minutes ahead of this traffic and at 37000' on the same track suggested perhaps he was sitting in his wake turbulence (remember vortices descend at about 500'/min).
The chap thanked him for the information and suggested he had tried cruising 500' higher and it was much better. The frequency was then bombarded by others wanting to know who he was and why he was not adhering to is cleared cruising height! He decided not to offer the information.
I hope the American pilot in front of him, who was one of many asking for his callsign, took it further.