If at all possible, I leave my seat in the upright position. At the very least, I adjust it as little as possible.
On one flight from San Juan to NYC, there were children in front of us and they were particularly annoying with their seats, etc. Their parents were oblivious to their bad behaviour and seemed to encourage it. Finally, my usually non-combative husband gave up and slammed the back of their seats to give them a warning.
We even complained to a flight attendant. The looks on the parents faces was memorable, however, they still did nothing to correct their children.