First it starts with the bananas, he is used other words before,now it's just bananas. Next it will be conjunctions, sentences will be blocky, he will sound like Kevin from the office when he is saving up time to go-to SeaWorld by cutting down sentence length. Next it will be verbs, he will just be grunting and showing motion with his hands. This process with continue with Tanner's skiing being affected as well he will eventually stop skiing and become an alpinist, the simplest of winter sports. In a few years Tanner will have stopped speaking only spitting incoherent babble, his diet will consist of only bananas, his potassium levels rise making him antisocial. Tanner will eventually become a hermit of the mountains living in a cave.
Source: PhD in gender studies and I watch vsauce & Rick and Morty