I think Sky Williams managed to prove this pretty conclusively. ADC is just NOT that hard at all to play. Its a role that has some of the best objective damage in the game, some of the best items in the game and no other role has somebody in lane SPECIFICALLY there to make sure you don't die. Essentially you are just being babied for the first 10-15 minutes of the game.
So why are most AD Carry Mains I have observed, so arrogant?
I think it's because there's very little room for error as ADC. If you step out of position, you just die instantly and contribute nothing to a fight. Roles that are more CD reliant like tanks, mages, and supports can all at least fire off a solid ability rotation before they get blown up.
ADCs end up blaming team and such because they are so reliant on their team, and because they are under so much pressure not to make ANY mistakes in the late game (if your adc dies for no reason late game, you lose the teamfight guaranteed). At least, that's my analysis as a support main.
I understand that but the amount of time a 
or 
has spoken to me like utter s**t, for absolutely no reason. Because I play 
as a main and they want a tank for some reason. I do know what Karma does and does not counter, she is my main. Or because I do not buy 
as my first time when I have already fed them a double kill in bot lane. I usually will get a 
to compensate for the small lack of vision because I want to actually have better mana when I get back into lane.
As an ADC main, the role is probably hardest to position with (imo) and heavily team reliant, so when people mess up they like to act arrogant, because technically speaking they are the most important role. I don't know what else to tell you.
EDIT: That's interesting. I didn't expect downvotes for saying why ADC's act arrogant.
It's because of the mentality that they have to solo carry the game so they think they're the VIP.
somebody in lane SPECIFICALLY there to make sure you don't die
Lol, I've been playing support wrong, my goal is always specifically to make sure the enemy ADC does die. 
FTW
In terms of sheer mechanical demand within a role, ADC is probaby near the top just due to the demand that high attack speed kiting demands. Trying to kite with Kalista after you hit 2.0 attack speed is kind of brutal on your CPS, and even the most minimal mistake means death. At least as a tank you can make a mistake and probably survive because you can take that amount of damage.
Plus, ADCs always have champions like 
and 
and 
and 
and 
who are looking to typically kill your first, so it's kind of stressful having that type of pressure when you know if they touch you, you die instantly, even if you don't necessarily do anything obviously wrong. Mistakes that lead to death could be just being slightly too far away from your support or being slightly too far forward where any other role would be fine being positioned.
Based on damage output, ADC is usually among the top tier damage threats on a team, and if you die, you can singlehandedly concede any team fight because you're not there. That's a big amount of pressure to carry around. I've personally played very nervously in fights because I know if I die, my team will very likely lose the fight, and it'd be mostly my fault.
Not justifying toxicity; that's not a valid reason to be toxic. Also odds are high it's just the person and not the role. Stereotypes aside, most ADCs aren't dicks. They're just in a high pressure situation, just like everyone in a game of LoL.
Because a light breeze kills us at all stages of the game and we are responsible for our own survival the majority of the game because solo que players don't usually realize that we have a giant bullseye on our backs as our 4 pals dive in to every team fight. That was a long a long run on sentence. #Feelsbadman.
I hate that everyone uses this argument that "no other role has someone their to babysit them the whole game". Yes, that's true, but it doesn't matter. The enemy has someone there doing the exact same thing. If a mid laner had a duo que that went mid with them every game as thresh to make sure they won, and the enemy didn't have that then that would make it easy, but both you and enemy having that role there for you makes it really even. [slayer-jinx-unamused]
Or maybe toxicity is dependent on the player and not the specific role...
many factors come to mind, the first: for being the best dmg on a team with the best items you're target number one.
I wouldn't say it's the hardest to play but there's many things to keep in check while playing adc.
You think it's easy to play with another champion in lane that supposedly is there to protect you, well... some of the so called supports have no intention of doing so, some of them don't even have the tools to keep you safe...
You need to work in tandem with your lane partner too, if he's aggressive you need to be a bit aggressive too and try not to miss cs and try to ward what he won't be warding. If he's more passive then you need to keep yourself safe and try to cs as much as you can while trading from time to time.
Mid and top lanes deal with 1 champion in their lanes, adcs have to deal with 3... you also should be looking at your mana bar and at your support's mana bar, gotta make sure that when you go in he can follow, or if he goes in you need to make it worth by dealing as much dmg as possible.
A lot of lane related stuff is also a problem when you throw two people in a lane, if you and your support don't have the same mindset, bad things happen. For example if you wanna freeze lane and your support simply doesn't agrees, he'll push and there's not much you can do about it but ask as politely as possible.
On a teamfight you kinda need protection since you're the most valuable target (or one of them at least, even if behind) if everyone is a diver... adcs have an awful bad time.
I think Sky Williams managed to prove this pretty conclusively. Sky Williams talks and talks and talks until u think he is right, but if u think about his words, they are full of sht. (not always, but he is one of the greatest shittalkers on earth)
ADC is just NOT that hard at all to play. That's because League of legends is not hard to play in general.
Its a role that has some of the best objective damage in the game You still need your team to prepare for objectives
some of the best items only if you get farm, feed or lategame, otherwise items are meaningless. And still, they can get one shotted by any mediocre assassin
and no other role has somebody in lane SPECIFICALLY there to make sure you don't die. in most games i have to play adc I get a somebody that gives no shit about me dying, or wards, or objectives...
Essentially you are just being babied for the first 10-15 minutes of the game. You should be, in many games you are not.
So why are most AD Carry Mains I have observed, so arrogant? That's your interpretation. I think most of them are dissatisfied, because there is no other role that depends so much on the team game. All strengths you mentioned are only take affect, if your teammembers play for you. In my opinion, the better support wins the botlane, not the better adc. With any other role you are flexible, you can play around counters or ganks. The succes of an adc heavily depends on the beahviour of his teammates. Your main job as adc is to get farm and objectives. You can only archieve these goals if your team/support helps you to accomplish them. With other words: Adc is the most sensitive role in the game.
bullshit.
Difficulty is simply a case of:
(2) and (3) are pretty high up, for ADCs, and (4) if you want to play decently is also quite high. as an ADC, (1) is really lacking.
(1) lacking + 2,3,4 at high levels translates to stress and feeling of lacking agency.
Heres my view as a diamond mid/jg main
I think there are different TYPES of hard. Jungling isn't that much about mechanics, it's more about strategy and knowledge. Adc is hard in terms of mechanics
You can't really out-think your opponent as an adc. You pretty much rely on raw mechanics for most of the game which makes it the hardest mechanical role (tied with mid imo) while jungle is the hardest knowledge role (support close behind)
