In another game, I had a Soraka that thought having a Sightstone, not a Ruby Sightstone just a Sightstone, was enough wards on the map... 30 minutes into the game. I have had several posts about this before... Just because you have a Sightstone, does not mean you are warding. Actually, if you think that it is warding, you are hurting your team as a whole. Buy wards if you know what is good for your team.
I had other games where one player or even two players had given a easy win away because of their stupidity (can't state this in a nicer way) but I just don't feel like going into my history and re-gaining the feeling of wanting to bash my head into my keyboard.