When one's crap, AKA a deuce, is so big it cannot fit down the toilet pipes. It is neccesary to break, or chunk, up the deuce so that it can flush properly.
I ate some wicked Mexican food last night, and had to chunk up the deuce... twice!
A sunburn or suntan focused on the left arm. It is caused by the left side of the body being the only half that gets exposed to sunlight while driving. Presumably, it would be located on the right side of the body in countries where they drive on the left side of the road.