ok,
First, if you want to "goof off" with a champ you aren't great at there is a two word answer.
Bot games.
Just remember if you want to do something like first time Riven jungle when you aren't a great Riven player....
Bot games.
Or when you want to try out that free champ with a high difficultly level.....
Bot games.
Get the picture?
Honestly, you set yourself up for the abuse. You went into a match where your rank was going to dictate the level of teammate you have. This means that they expect a certain level of play and to a point they deserve to see you play honest and hard. But you came in with the idea that you were going to goof around with a champ playing way out of position and worse, with a champ that you admit that you aren't very skilled on. This meant you effectively made the game a 4v5 right from the start. It also sounds like you tried too hard to defend yourself and got both teams involved in the comments.
If you do end up playing poorly. You just say "Sorry, doing my best". If its a new champ you can say that, but don't say more and don't talk back a second time. Mute, and play the best you can. If you keep responding, the rest of the team will get more toxic because they'll see it as excuse making. It will have them thinking you are trolling them so you can laugh about how you caused them to lose the game.
I did once try a first time champ in a normal and played very poorly early. One of my teammates spent most of the game berating me. I tried twice to calmly say "sorry, second time on this champ." and after that just ignored him. The rest of my team was actually very nice because I didn't make excuses. Just tried hard.
There are going to be "salty" players and trolls. This weekend I had 2 incidents that stand out to me.
First, I wanted to try out Nidalee since she was on free rotation. I went into a intermediate bot game and told my team in the champ select lobby that I was trying first time Nidalee. When I made a mistake and gave up first blood I immediately typed. "Sorry, my bad." Two of my teammates responded by typing. "No problem, its just bots." They understood and were not critical about my mistake. This is why I use bot games to try out champs. Even with me struggling we won easily. And it was overall a positive experience as I was not condemned for my struggles with a champion.
The second was a team builder game. I belong to a teamspeak community and a friend of mine asked me to join him while we helped 3 under level 20 players get into the game. (one just level 5) [I'm level 27, my friend is level 23]. We ran into a troll team that included a Silver 5 ranked player and which without telling us they weren't playing the game straight this team played the game as a giant gankfest. They roamed as a group of 5, coming and ganking our less skilled players again and again. I had taken Cassiopeia mid and did not face anyone in lane at all. Neither did our top laner after the initial 5v1 gank at level 1. This game was not fun for my side at all and worse the conversation in the post-game chat was the definition of trollish from the other team as they laughed about how they "rekted" us thanks to their 5v1 pattern. (not to mention a level 29 playing Veigar and a level 30 silver 5 Nidalee.) It was a very negative experience for my side. Fortunately, the newer players are adults and they took it as a learning experience rather than ended up down on their performance. My team handled this group of jerks. (and there is no other word for them I can use in polite company) We did it simply by not engaging in chat and leaving the post-game chat quickly. Talking to them was useless.
