Bumptious describes people who are rudely and often noisily confident or over-assertive. It can also be applied to actions or behaviors that show this same attitude.

// Our host apologized for the bumptious party guest who caused a scene before being asked to leave.

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"She comes across as a bumptious, irritating ten-year-old who believes that her main vice, her steam-roller self-confidence, is a virtue." — Lloyd Evans, The Spectator (London), 17 Aug. 2024

While evidence dates bumptious to the beginning of the 19th century, the word was uncommon enough decades later that Edward Bulwer-Lytton included the following in his 1850 My Novel: "'She holds her head higher, I think,' said the landlord, smiling. 'She was always—not exactly proud like, but what I calls Bumptious.' 'I never heard that word before,' said the parson, laying down his knife and fork. 'Bumptious indeed, though I believe it is not in the dictionary, has crept into familiar parlance, especially amongst young folks at school and college.'" The word is, of course, now in "the dictionary"; ours notes that it comes from the noun bump and the suffix -tious, echoing other disapproving modifiers including captious ("fault-finding") and fractious ("troublemaking").