1
general::
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]
American Heritage Idioms
2
general::
Phrase(s): fly in the face of someone or something [and] fly in the teeth of someone or something
Fig. to challenge someone or something; to go against someone or something. • This idea flies in the face of everything we know about matter and energy. • You had better not fly in the face of the committee.
McGrawhill's American Idioms And Phrasal Verbs