Sh*t people do, that p*ss people off
This is going to be a relatively long wall of text, followed up by numerous more giant walls of text. Predominantly in most cases, it has to do bad decision making, usually followed up by, more bad decision making.
1: Taking farm that doesn't belong to you. Why oh why, do people think it's their God-given right to snowball their ADC lane at level 1 by challenging Gromp or Golems? Gromp and Golems are crucial to a jungler's snowball, especially when they're already crippled enough as it is to begin with. You're hindering them, EVEN FURTHER. Stop it. Yes, I realize some junglers come to your lane and they take your lane minions, and you somehow feel it's justified to get your revenge on innocent jungler in your next lane. WTF? How does that even make sense?/
Vice Versa. Junglers. Don't take lane farm obnoxiously if your laners are ALREADY in the vicinity and are trying to last hit. It's obnoxious and it's putting them on tilt. It is acceptable to farm lane minions if you are NOT that lane IF the laner is away from their post or if the creeps will die to tower anyway. Look up the definition for static farming, if you don't already know it.
DONT TAKE JUNGLE BUFFS WITHOUT PERMISSION. EVER.
What the fuck? If a jungler isn't even level 6 yet, assume he does not want to give you his jungle experience / gold. The jungling item gives additional gold per slay of large minions. So stop slaying, the large minions. If you want to 'assist your jungler' to damage the large minions, do just that, help leash them, but don't diligently take the last hit. Why the hell am I leashing something I would get a bonus from, to an ally who wouldn't receive the bonus? I'm NOT DOING IT. So stop assuming i'm being a nice guy. I'm a fucking smurf, who is more than likely carrying you with my supreme decision making skills.
Do you think that you would benefit more from the blue of red buff than your jungler will? Then ask them, if you can have it. Ask for permission. More often than not it doesn't suit your jungler's plan of action that he is brainstorming, and now depending on who they are, they have to dodge the next team fight because they are physically incapable of participating in it. Generally has something to do with some teammate, who made a bad decision to take something that didn't belong to them, without permission.
2: Calling Shots.
First of all, your jungler (the role with the smite) should call shots on objectives such as Dragon, Baron, Jungle buffs), unless they are out of position and it can be challenged safely. Half the time if a non-jungler calls a shot on Dragon when the jungler doesn't have smite available, they could know that it's unvaluable to challenge, yet gets blamed anyway when the enemy jungler smites it, because his or her teammate continued to challenge it without the jungler calling the shot. Objectives such as Dragon / Baron, should ALWAYS be called by the jungler.
Enemy kill order:
Jungler (If challenging Dragon / Baron - otherwise exclude) Highest damage dealer -> Lowest damage dealer. Most destructive CC -> Least destructive CC.
Generally involves shutting down whoever is carrying for the enemy team, followed by ADC, followed by APC, followed by Top/Jungle, followed by Support.
LoL is NOT a first person shooter. Your objective is NOT to attack the closest target to you, but following suite with the list I have describe above. I don't know how many times i've seen my teammates burn their abilities on the 10-25% HP tank, instead of the enemy damage dealers.
3: Thinking your ADC is the person who should peel for you.
What the fuck??? Yes your ADC wants to be a contribution to the team fights, but by no means do they want to be the front line because you decided to leave them behind to fend for themselves, for no particular reason. Bad decision making, generally followed suite by the allies who left you to fend for yourself, now re-engage because it seems more appealing.
Rule #1 to moba gaming: "If you do not participate at or during the time when your allies participate, and they die in combat, under NO circumstances, should you engage in combat." There are so many reasons why this is a VERY BAD decision. If you don't want to engage, don't engage, but BACK UP, and don't die. Nine times out of ten, if you retreat from a team fight and your initiator dies, and you re-engage, you will die, the enemy team will miraculously snowball out of control, and the game will be lost.
4: Not being proactive.
A: Not using Summoner Spells when you should. "You had Flash / Ignite / Exhaust / Heal up the entire time and you didn't use it?" Sigh... B: Sticking around near danger for too long. You're going to be the primary reason that your lane opponent tower dives you for a non-contested free kill, and no "baiting them" wasn't the appropiate decision, you dun fucked up, that's what happened. C: Not initiating on opportunities when it's most prime to do so.
5: Acknowledging a gank and then refusing to follow through with it.
Like seriously? I already have to deal with unskilled garbage, now I have your stupid fucking psychological, i'm pinging your lane opponent, and perceiving to you that I am going to engage on them, and then i'm going to refuse to actually fucking do it? GO HOME, and get the fuck out of my matches. Seriously, you are only convincing Riot that you are not trolling, but you aren't convincing anybody else.
6: Requesting assistance, and then abandoning your teammates whom you requested assistance from.
So you're saying, I can't farm, because you want me to die in team fights, so that YOU can escape safely? Well why didn't you just shout that out instead of making it seem like you actually wanted to try to win or be a team player? In which case, I would have gone about as far as humanly fucking possible away from you, and refused to participate in team fights.
Fucking douchebags.