Why a lemon?

If anybody has some spare time, feel free to search the 532,000 photos on Google to answer a pressing question:

Why are there about 30 pictures from Saturday night featuring a lemon? For some reason, one of the guys my buddy brought out to the bar insisted on having this f#%&@&ing slice of lemon in every picture we took. Usually blocking the subject of the shot. Why would somebody do this? What the hell was wrong with the kid? Inquiring minds want to know.