Have you tried wearing it with either full jersey pockets, or the with something in the pocket on the jacket? You might find it's no longer flappy under those circumstances... ?
@Rod_Munch started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
Have you tried wearing it with either full jersey pockets, or the with something in the pocket on the jacket? You might find it's no longer flappy under those circumstances... ?