4 man premade in solo ranked

Why is this allowed? I was just bullied in champ select because I banned Malzahar. They told me they would troll. And take my lane, etc. Proceeded to pick Cassiopeia for jungle, without smite, and then told the other team that I was trolling. So about 3 minutes in they come to take my lane, so I say fuck it and start feeding. I realize I should be reported for this. But what the fuck.