Can you get banned for PMs

If you knowingly add them, when they are not your actual friend, and they proceed to flame you, then that behavior is generally not punished. You should not add friends who you are not willing to communicate with in a "private" manner - as in without oversight.

If there is some extreme toxicity in the PMs, it may be punished. But private messages are simply a tool Riot provides for users to opt in to communicate in private with each other. They are not moderated.

If you reported them in the post game, that should suffice to have their actions looked into (I've rarely had someone PM me who wasn't already rude in the game).

They generally do not punish for private messages, since they are opt-in experiences. But as Rujitra said, if it's extreme, you may want to report it in a support ticket.

yes submit ticket

You are invited to report inflammatory players, best to take screenshots for these kinds of scenarios.

That someone is your FRIEND, you accepted his FRIEND request. You talk with your FRIENDS as you like, so no, it's probably not punishable. But you know you can UNFRIEND your FRIENDS if you do not like them. You do not have to call your dad (sorry, i mean Rito) to get rid of your FRIENDS, since you can do it by simply pressing one button (actually 2 or 3).

I disagree with this idea that an Opt-in experience is not punishable. I would be interested in the post where people got this idea from.

It is similar to the argument of "Just mute them", you can simply "opt-out". But that argument very clearly doesn't fly, and is not an excuse for toxicity.

If you take a screenshot of their dialogue and submit a support ticket, I would think Riot would look into it. If they do not punish the player for the PM, they can certainly look into their games and will most likely find similar behavior. I recommend you do so, I would be interested in the outcome.

I think unless they threaten you physically you cant really do much about it. Riot doesnt monitor PMs.