I understand the point that you are advocating but generally I don't think it is going to change the personalities of people who do play generally not nice. Although it is great advice.
One thing I would like to add is don't let these people get to you. What I recommend is having a positive mental attitude while playing. Like Ellohime says, we all have giant dicks and for the ladies very tight vaginas (don't really know how this relates but still going with it). If the people you are versing are being annoying either ignore them or mute them and move on. Don't let them get the best out of you.
I have recently been playing with a new controller and having hard time adapting to it. I got semi consistent with the xbox 360 controller and obtained a "high skill rating" (not like super good but consistent in a sense) with it, but with the xbox one controller I haven't been able to have the same consistently and now playing with these same high skill people has been quite a challenge. I basically have been making a lot of mistakes (well I generally make a lot of mistakes but its been really bad lately). I almost always will go @$?!, Whoops, the occasional "lol" when it is really bad, or Sorry! after making mistakes to basically say "my bad" to my team. Usually will get no response or a No problem. Sometimes the sarcastic remarks come but I take them as joking/playing around. If I find myself getting a bit annoyed (which is a bit rare because again PMA is where it is at), I'll just mute and move on. No need to have someone try and put me down. If worst case scenario comes and the guy/girl is being a little fuck boy (a term RhinoCrunch uses that I think flows pretty well) (like saying some really awful things) I'll again just mute and move on. Like very recently versing this team of three and I'm playing very poorly. Teammates quit on me (thankfully it was unranked so bots came in) and its like 4-0 with really no hope coming back. One of the opponents just goes "James just gtfo". Well I muted and stayed. Ended up losing but still had fun. Played more matches with the same party of 3 and won some and lost more but oh well.
I'll sometimes play with couple of my friends who are much better than myself and in steam I'll tell them if I'm not feeling it or I'll tell them I feel like I'm playing like shit to give them a heads up. But I still will have PMA while playing the game (in this case of playing poorly I'm learning what not to do when playing rocket league ha).
When I drink it is a bit harder for myself to have PMA and I admit I have said somethings I regret like one that sticks is calling someone out for playing not so great and being a little bitch to him (I wish I could say sorry now) and another time when team mate was giving me advice I took it the wrong way like him calling me stupid and I said "no shit" to him which again wasn't very nice. These moments were months ago and I generally don't drink and play rocket league any more.
Overall though just have fun!
On side note, one thing I would recommend Psyonix adding to the game is to have the player choose what type of player he/she is for the casual game modes (maybe put in options menu as a drop down list). So first the skill rating/mmr takes in place, if there is a large pool then search the pool to see if there are similar player types and pair them together. If there aren't combine with other players also taking a bit to find a match together. Just to help get the people who take the game more serious, people who just want to relax a bit, or people who are drunk get pooled together. For this to really work well would need a large player base (not saying RL is small but it sometimes does lack number of players playing (specially at night time)).