Going to someone elses house and finding:
Dripping taps.
Doors that need adjusting.
Paint on lightswitches.
(at least the old Vertical Hold doesn't need adjusting)
In pubs - press down taps that are impossible to use as they won't stay on for a few seconds.
Worst I saw after trying to shut off a dripping tap was that the Hot and Cold knobs were on the wrong taps.
Anyone with any others or have I got OCD?