If the other team has an actual Intentional Feeder......don't kill the feeder.
Just let them walk under tower to execute themselves, or just avoid them.
This is what I do when there is someone who is actually intentionally feeding on the enemy team (running it down mid, saying in all chat "come kill me", etc.). The enemy team is already going to be down one man pretty much all game, and we all know the feeling of having a feeder on your team.
So, show the enemy team a little courtesy by basically saying "I know this guy sucks, and I'm sorry he's doing this. Thus, I'll make him powerless."
Granted, the enemy team will still be playing a 4v5, which is next to impossible to win these days, but, at least you make it a bit easier by not making it actually impossible (and yes, I know, people have won with feeders on their team).
Of course, if the feeder decides to actually play the game, and starts to try to kill you (even if it does involve running into your entire team alone), then defend yourself, and start killing them. You don't want to end up feeding the feeder, than having them carry the game for the enemy team in the end. Cause that just makes everyone's day worse, even for the enemy team.
Just figured I'd throw that out there.
and taunt me under my own tower?