The reason is more function than fashion, according to CBC Olympics snowboarding expert Craig McMorris.
"Sometimes those bibs can fly up in your eyes. That's very, very dangerous. So a lot of the riders will tuck it under their arm," McMorris said during the snowboard halfpipe competition.
The use of the one-arm method of wearing the bib is not universally adopted. Gold medal halfpipe snowboarder Ayumu Hirano of Japan didn't use it. But Chloe Kim of the United States did as she won her second snowboard halfpipe gold medal, as did New Zealand's Synnott Sadowski on her way to snowboard gold in slopestyle and silver in big air.
Some snowboarders made other fashion statements.
French snowboarder Lucile Lefevre was a crowd pleaser at Big Air Shougang when she wore a tiger costume during qualifying. Lefevre was injured and knew she couldn't do the big tricks necessary to make the finals. So, she borrowed an orange-and-black big-cat costume from Swiss snowboarder Nicolas Huber. Why Huber had it is a mystery unto itself.
Then there was U.S. snowboarder Julia Marino and her board with a Prada label on the bottom. Marino won silver in slopestyle, but later dropped out of the big air competition. She said on social media the International Olympic Committee told her to cover the Prada logo on her board with marker.
Marino said doing that would have affected the function of her board, so she dropped out.