Over the last little while I have had people honking their horns at me and being particularly cross for what seemed like no apparent reason. They would give me gestures along the lines of "what do you think you are playing at?" and I would reply with my gesture which meant "can't you see my bloody indicator - moron?" Turns out my near side rear light cluster had fallen out of its socket and was resting out of sight in the lower cavity. As a consequence my left indicator did not blink to the outside world. Very, very sorry.