Americans usually trying to walk on the right and the visitors from Japan et al trying to walk on the left.
Happens all the time in UK/Europe. It's a strange carry-over from driving left or right that pedestrians tend (mostly) to also favour the same side . A further corollary is that you'll tend to swerve that way to avoid collision, which leads to many "Sorry!" "Sorry!" moments with oncomers from across the water.