impertinent

/ɪmˈpʌrtənənt/

/ɪmˈpʌtɪnɪnt/

If someone's rude without being openly nasty, like a kid in the back row of class quietly heckling his teacher, you can call him impertinent.

Impertinent originally meant just what it sounds like, "not pertinent, irrelevant," but it also came to mean "inappropriate, out of place" and therefore "intrusive, presumptuous; behaving without proper respect; insolent." It still carries a condescending air, so it's best used of or to a child being snippy to a grownup: "Don't be impertinent!" The stress is on the second syllable: im-PERT-inent.

Definitions of impertinent

1. adjective

   improperly forward or bold
   “impertinent of a child to lecture a grownup”

   synonyms: fresh, impudent, overbold, sassy, saucy, smart, wise

   forward

   used of temperament or behavior; lacking restraint or modesty
2. adjective

   characterized by a lightly pert and exuberant quality
   synonyms: irreverent, pert, saucy

   spirited

   displaying animation, vigor, or liveliness
3. adjective

   not pertinent to the matter under consideration
   “mentioned several impertinent facts before finally coming to the point”

   synonyms: extraneous, immaterial, orthogonal

   irrelevant

   having no bearing on or connection with the subject at issue