Well, first let's look at the things you listed off that other players do, and see what's okay and what's not.
- Play Ranked matches as Champions they've yet to play prior.
Is this a bad practice? Yes - since it can lead to a loss fairly quickly if the player isn't adaptable, but it isn't forbidden. Players can play who they want when they want. Sometimes they might even find someone they're good with.
- Pick something off-meta (sic; "a champion in a a lane that is not supposed to be played there").
This has something of a middle-grounds, because there are no explicit rules saying you can't play whatever you want wherever you want. But, you do have to communicate your intent with your teammates, and be ready to change tactics and do something a little more normal every now and again - elsewise you end up with stuff like "Support Nunu" and "Support Singed" that's earned many a player's ire, and the off-meta player's punishments.
- Flame from game start to game finish.
This is very much against the rules. If you see someone doing this, report them post-game. They will get punished.
Regardless of situation, this is also very much against the rules. Again, report whoever you see doing this - there's a little less possibility that they will get punished, since gameplay-related offences are a bit harder to catch than chat-related offences, but don't be dissuaded from reporting them. Repeat-offenders will get punished, heavily.
Now, let's look at what you did that netted you a punishment.
- Told someone to kill themselves.
This isn't right, at all. Ever. There is no reason for you to tell someone to hurt themselves, let alone kill themselves. You are playing a game. It's not any bit greater than a human life, but for some reason you place higher value on a 25-30-minute affair than human life, and for that, you get a fittingly harsh punishment.
Riot punishes anyone who encourages self-harm with an immediate 14-day suspension. You should honestly know better than to say something like that to strangers. You wouldn't walk up to some random person on the street, only to continually deride and belittle them over nothing, telling them they should end their life, would you? 'Cause, in the most basic sense, that's exactly what you did to get your ban.
And, I'm a fairly active member of the community myself - I don't build teams, for sure, I'm a solo player, but I'm still fairly active. But, how active you are in the community, your presence in Reddit or ESL, or whatever other site that "contributes to keeping the game alive", is completely beside the point.
In fact, I'm pretty sure that all the sites "keeping the game alive" would probably abhor someone encouraging another to kill themselves, so I wouldn't try to leverage any part of the community in your defence, when they just might agree with Riot on your ban.
And, no - telling someone to kill themselves doesn't make you a flamer - it makes you an awful person who really shouldn't be allowed to play the game. If this is your first offence, you had best learn from it and fast, because your account is one step away from a permanent ban. There are a ton of options you can use to help prevent this, though;
- Learn restraint. If you can't chat with either positive speech or gameplay-oriented chatter, you should keep your hands on the mouse and the buttons for your abilities/pings - sometimes just your abilities if you're the kind of jerk who likes spam-pinging "?" pings whenever your teammates screw up.
- Learn the function of /mute chat, /mute pings, and /muteall. These things exist for a reason, and - before you say it, no, they do not exempt you from punishment if you decide to tell a muted teammate something awful. They're there so that you don't have to tune in to your flaming teammates so you can focus on the game. Use them freely.
- Just don't use the chatbox, period. If you can't show restraint, don't press Enter. Just keep your hands on the gameplay keys, and play the game.
All in all, you - if you're organizing teams for tournaments - should know WAY better than to tell someone to kill themselves. That is abhorrent, horribly unprofessional, and you probably should be removed as the organizer for your tournament team(s) for such a horrible thing. Seriously, it's a friggin' game, there's no reason anyone should have to be told to kill themselves.
The only other thing I can really leave on with this is the famed Golden Rule of Christianity; "Do unto others only as you would have done unto yourself."
Think on it, and serve out your sentence. The fortnight off League should do you good.
