Different Brands of Fun
We all have different ideas of what is, and what is not, fun in League of Legends. Some only play ranked, others Twisted Treeline, and still others who only play ARAM. There are those who like Summoner's Rift, but do not play ranked as they enjoy a more relaxed gameplay.
No matter what you deem as fun, this does not give you the right to drop into one of the other modes and purposely troll, int, or harass the players who enjoy that mode. You may feel that the rules only apply to your choice game mode, but this is simply not the case. "It's just (mode)..." is the exact same as someone doing it in Silver and Gold and telling you "it is just" low tier play, or trolling during your promos because it isn't THEIR promo.
You get irritated when people do it in your mode of choice, so why do it to someone else? If we all followed this one, extremely simple, rule - the community as a whole would grow a few notches towards not being seen as the worst in gaming.