Someone who is too "straight", "clean" or "square". Two possible etymologies. In Australia: originally a developer who chops down wattle (Acacia) trees, taming the wilderness. Everywhere else: originally someone who uses Autotune. If you gently karate-chop your adam's apple when you sing, you can sound like you are using autotune.
Have you ever seen Joe bust a move? I haven't either. He must be a wattle chopper.