I like competitive games sometimes but have never been so competitive in them that I have joined any teams or clans or whatever one might call them.
IMO if people join a random group, say joining random games on CoD/BF3 or joining a random PvP match on an MMO or whatever, for the most part people should realize that there will be a wide range of skill differences, age differences, personality differences, and you just need to enjoy the game.
The only exception to this is a game like Monster Hunter and others like it where if your group fails you don't just fail that mission or lose the game and then join another one without any real penalty, you lose your own personal materials (health packs, potions, food, grindstones, money, everything). Every single fail your party gets directly effects your own personal resources that you personally had to grind for hours to get, spent money (in game money) to get, and all around took your time to achieve.
Monster Hunter isn't "competitive", but it's "online", and if you join a High Rank random group where everyone has to use their own resources, the game doesn't give you any, then you should be prepared to be called an assface if you wipe the group out of your inability to play properly (you play Low Rank first on the same basic bosses so there's no excuse to not know how to fight them) - don't join High Rank if you aren't competent enough to play it, you are just ruining everyone elses time and wasting hours of their grinding materials.
Basically - generally speaking relax and just have fun, most games this is the case - but there are defintiely certain times when you need to step back and realize you are ruining the fun of others either on purpose or not, and you need to learn the game better before joining higher ranked modes.
“Anna, my strong, terrifying Anna.” -Cas
"You lack the requisite spine and testicular fortitude to study under me" -Elodin