pros do that. streamers do that.
While on camera they will often say stuff like "this guy is complete trash", often times they only verbally say it. It's not like they actually write in chat "u suck lol". As long as you keep quiet ingame it is fine.
That's not to say that they don't write in chat at all. It could be Rito is just a little more lenient when it comes to pros and streamers, but that's just a theory.
if u do that (even with ur premade friend) the system just mark u as toxic and u get banned every 2nd game u play.
The poor bot doesn't know any better. It doesn't understand sarcasm or how trash talking works.
And usually, unless someone reports you it is unlikely you will get banned. So whoever you do trash talk either got offended, or the players are not sure if you're trash talking or simply being toxic.
So even if you're trash talking a friend, don't do it in chat due to reasons above.
"OMG GL HF LOVE URSELVES ENJOY LIFE YOU ARE BETTER THAN U THINK U R AND U R BEAUTIFUL PERSON"
I would find it cringy and hilarious if someone actually wrote this in chat.