So what am I to do when a summoner does this

In my last game, we were well on our way to a stomp until.. FOR whatever reason, this fizz calls us trash, then proceeds to run to their fountain and execute himself..And then started building tank, just starts inting.. 1v2-3-4-5, not backing when low.. running around the map doing nothing..

Simultaneously... Our Nid jungle starts dying alot.. I was all for her just playing bad until me and the Nami got back to back stuns on the enemy team mid in wide open lane, no minions, no body blocking... AND SHE DOES NOTHING!! she runs in after me and nami back and dies..

I looked up both these players history... they don't have a history of inting so I'm just sitting here like, what the fuck.. WHY!