Also, fly in the teeth of. Act in direct opposition to or defiance of. For example, This decision flies in the face of all precedent, or They went out without permission, flying in the teeth of house rules. This metaphoric expression alludes to a physical attack. [Mid-1500s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.