I mean, that's just called trolling.
A troll is someone who deliberately acts in a way to cause other people to get frustrated, annoyed, etc. A league troll wants you to flip a shit at them because they know Riot is much better at detecting chat offenses than gameplay offenses.
So yes, bait banning is real. It has been a thing for as long as internet interactions have been real and presumably for centuries or millennia before.
You can send a ticket to support, informing them that Player X admitted to trolling during Game Y at Time Z. They'll give a non-committal "hey, thanks for the report", but they DO accept reports of trolling via support ticket.