What to do when people purposefully try to ruin your game

I played this afternoon with a friend of mine (who's still a beginner), and two times we had our game ruined by people who decided we shoudon't have fun. The first one, just after we remaked because of an afk, someone flamed us in lobby because apparently the ago guy was his premade. He flamed us hard then right before the end said "no way I will I go mid" even though I had called and picked mid for 40 seconds (and picked already). In game, since he indeed go mid, i let him in order to not ruin everyone else's game and go will with my friend, playing adc. You can guess that with a fork support without support items (and a beginner), things didn't go well for us. We got rekt by the enemy jungler who saw easy kills and couldn't farm. Meanwhile, that player who flamed and trolled had easy lane, with help from our jungle got pretty fed and had a great time. At the end, everyone wanted to report us for "feeding" thought I was the good guy, making so that other people could play normally.

Second game, in draft, I banned yasuo without having seen that someone wanted to play him (you know, the rush when the countdown reach 0). I said I was sorry but no way, he flamed and went level 1 under t2 not to give an early kill to our opponents (we were playing the botlane). Then things go again, we make good early but with first blooded opponent and then having 3 slayers in our team and 3 in the enemy team who just saw in us immobile people without protection and far behind, we just spent the game getting flash-ult by wukong or zed. You can guess we hadn't a great time. The troll however did fine.

You can add to that a game ruined by a Fizz jungle who inted because he didn't get pull and decided he wouldn't hank nor help anyone (and a 0-9 draven top)

Now the question is : What to do when someone wants and succeed in ruining your game ? I mean purposefully, from beginning like the two above. In real life you would punch them in the face and everyone else would kick them out and find another player. Here you can't do that so you tey to do the best for everyone, even though you know you'll probably have quite a bad time. On top of that noone cares... You should get support from other players, maybe honour or extra help from the jungler but in fact the only things everyone cares about is who is feeding or not. So at the end the person who ruined your game, very proud, call to report you and everyone follows.

So what is the point ? What is the incentive to be the nice guy when in finne everyone proves to be unfair dicks ? Next time I just stay mid and let someone getting rknt 1v2 bot ? They will have fun. In fact, why do you even have to play with such people, a game you know in advance you won't have fun doing ?

Obviously I reported them, but didn't get the popup that my report has helped. So tell me, what should I have done ? Should I be selfish since I'm right, even if it has to ruin everyone's game ?

What could have I done so that both times I wouldn't at the same time have a way worth time than the troll AND looks like the bad guy to everyone ?

Thanks for reading, also Red advice much appreciated

P.S. I know it's the holidays, and a lot of annoying selfish kids are playing, but maybe there is something to be done about that too.