Toxic Player

Good Afternoon, I recently played in the rotating game queue and I came across a very toxic player, I brushed it off. Post game screen he decided to friend me and in my naive thoughts I was hoping her would apologize.... I was wrong. The player started spamming me saying how bad of a player I was and why I myself make league a bad experience for everyone else, other things such as calling me a "loser", saying that I have no life and should "piss off" and quit playing league. Is there any way I can report him, even after closing the post game screen? Because I have a feeling I wasn't the first, nor will be the last to be ridiculed. If need be, I have chat logs and the players name readily available as proof, as well as my own chat logs that show no forms of aggression, or misdemeanor. Stay -y -Shevans