Intentional feeding usually works a bit differently in ARAM. Most of the time, someone's low on health and just sits around waiting to get to full health even though they don't have a good reason to wait around and when a team fight breaks out they simply do nothing. That's basically feeding their allies into the enemy when they had something to contribute to the fight.
And of course there is tactical feeding, which is very different from intentional feeding. You go and get yourself killed by only one enemy or at least not the entire enemy team to minimize assist counts and gold gain for the enemy. Or even better, get executed which actually isn't feeding at all unless you get caught trying to do it.
If half a team or more are just running past towers, not even trying to push by destroying buildings/minions/champions, then yeah, that's just bad manners and I'd report that...but I rarely see it myself. It's just going to be like 1 guy maybe and it's easily identified as a robot player.