In the sport of triathlon, it describes a competitor who's conversation has become boring due to their incessant talk about the sport, past or upcoming events, training, diet and all things related to triathlons.
We had dinner with Steve yesterday, he's looking great but all he talked about the whole night was triathlon.

I know, its painful. He's become such a tribore.
by Drew Peacock9 February 20, 2012
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