Shortened term for an extremly large shit. Originating from the phrase "shit the size of montaña". Montainya is to be said with a country accent and is a combination of the spanish word for mountain and the state of Montana.
Guy 1: Wow it smells so bad in the bathroom.
Guy 2: Haha thats cuz i just took a montainya.
Guy 1: Damn ur asshole must be ripped and bleeding.
Guy 2: Yea
