Champion Select toxicity (what can be done?)

As the title implies; I understand for not being able to report someone for post game chat. it's voluntary to stay after the game. But pregame chat can be more toxic than in game because there isn't even an option to mute a player. This player I recently queued with not only trolled by banning the champion I wanted to play but he also said he was going to int just so I would lose LP and repeated told me to kill myself as well as giving instructions on how to do so. Something should be done about this because it's very frustrating to come across this type of player who wants to ruin games before it even starts and leaving isn't always an option (whether it be because you've already done so before or if you're just in promos). You get punished for trying to distance yourself from these types of players pregame so i'd really like to know if something can be done to avoid this because i come across it commonly, although nowhere near to the extent of this particular player from recently.