In Rocket League, using the quickchat is the simplest way to destabilise oponents or express discontent about your teammates.
You can use quickchat for meaningful comments about a teammate missing a save or a shot, but you can also spam it without toxicity, with messages such as "Nooooo" or "Wow !" it to disturb weak-minded players.
Quickchat will not make you banned, doesn't make you use much brainpower and will not significantly disturb your gameplay, it really is a good tool, use it at will !

Writing Rocket League chat can get you a game ban really quickly if you're not careful.
You need to understand how report system is working :
Reported messages are handled by bots, if they contain swear words you get a ban.
To avoid bans you can either not use swear words as insults, or alter swear words to avoid being parsed. The latter is risky because some variation of your swear word may get detected.
Thus, I would recommend being toxic without swear words, of course it doesn't diminish the level of toxicity you can reach.
And I believe non-english swear words will not be detected, make use of your language skills !

Also, I think you really shouldn't be reaching your keyboard to chat during gameplay, toxicity is part of gaming, but gaming is... gaming, and making an innocent teammate lose because you're arguing instead of playing doesn't feel right to me.
Only use the chat after scoring a nice goal or winning the game, it feels even better !

You've been playing well, thrown a few "What a save" but now a crybaby player is trashing the game ? Use the report system at your advantage !
Reporting a player being afk or own goaling for "unsportsmanlike conduct" will have no effect.
You're better getting the player to use swear words and report him for "verbal harassment" and you will be making Rocket League a better place !

Destabilising the opponent team with your behavior is part of winning.
People getting disturbed by chat messages have a very low level of psychological resilience, and you will of course win way more easily with grown up people in your team than immature teammates crying because of a few "Wow !"
If you and your teammates have been "what a saving" in harmony after scoring sick shots, it's time to party up for a win streak !