The definition of bumptious is someone who is proud or self-assertive in an obnoxious or irritating way.
A businessman who is always talking about how smart and rich he is and who is constantly telling you why he is the best person to manage your business is an example of someone who is bumptious.
Crudely or loudly assertive; pushy.
Disagreeably conceited, arrogant, or forward.
Origin of bumptious
Probably a play on the pattern of words like fractious.