When a certain airline was in the early days of operating the A320 they suffered a spate of incidents with autopilots disconnecting and also an uncommanded roll. The engineers scratched their heads and it started occurring on different aircraft. The problem could not be replicated by the engineers but following a lot of component replacements and trouble shooting the problem was narowed down to one particular pilot.It transpired that he was crossing his legs and knocking the stick with his foot. He was completely unaware that he wss doing it, but once he was made aware the problem never reappeared.
There have also been problems with crews placing teas etc on the pedestal next to the stick, and the contents being dislodged into the mechanism underneath it.
Side Stick Controller Photo by Jetdoc1 | Photobucket