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An overboner occurs when an individual becomes excessively distraught or animated over an insignificant matter which other individuals do not find congenial.
Mrs Marsten in Tuesday Period 5 Chemistry lesson following Physical Education when a handful of people are quietly whispering about the lesson's work:

Stop talking (getting stressed). DANIEL SHUT UP! TOM MOVE TO THE FRONT. STAVROS FUCK OFF!
by Rob Dodds March 05, 2005
Having an overboner is getting overexcited or stressed about a fairly trivial event. i.e taking something too seriously.
Edward Law (at lunchtime soccer): Come on guys, we're losing, COME ON!
Rob dodds: Meh
Ed: NO, we need to start playing, you're all so shit
Everyone else in unison: SHUT UP ED, don't get an overboner!
by Big Penis February 24, 2005