Informant is a descendant of Korean immigrants who moved to the states in the early 80s and now resides in Utah.

Superstition as told by informant: my mom said not to shake your legs or you’ll lose money. I’m pretty sure she told me not to shake my legs because it was considered impolite in public, but this was just her way of getting me to stop shaking my legs.

In Korea your legs symbolize wealth and prosperity so shaking them is a sign of shaking your wealth off.

I did some research and could not find anymore on why legs are associated with wealth, but it seems like a tactic used by parents to prevent their children from creating the annoying habit.