armed to the teeth, fully prepared
Estou armado até os dentes de argumentos a favor do projeto.
I am armed to the teeth with arguments in favor of the project.
Multiple theories compete: (1) a reference to armed pirates who held daggers between their teeth while climbing onto ships, memorably depicted in 17th–18th-century illustrations; (2) a generalization of any soldier carrying so many weapons there's nowhere left to put them but in the mouth.
Source: Etymonline — teeth.
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