If you want to compare stats with your friends, just check in your in-game profile (mostly for ranked games). Or use pages like lolbase.net (for normal games).
League of Legends is game, where K/D ratio doesn't say anything about player skills. In CoD killing enemy is the most important skill in game. Here, what you need the most, is helping your team wins. And that means you sometimes will have to play support, who will need to do whatever needed for other players to get kills, gold and xp without dying, while you get nothing and ending as easy pray for enemy team. So you might end with horrible K/D ratio and yet be that person which gave your team a victory.