Let's list every way to int for science
Picking the wrong runes on a tank or melee support
Not picking the right runes on a tank or melee support
Playing
Letting
get to lategame
Playing as a squishy immobile mage vs.
or
and not playing perfectly
Dying as a jungler to jungle
before 5 minutes
Feel free to list more! Let's help out our fellow newbies.
Bonus Category: champions that are impossible to int with: 

to win the game so it wont matter how much your team feeds