Is there a possible way to report someone out of end game screen?

I just played an ARURF for funsies y'know and afterwards a player from the enemy team tried to friend me post game when I had left. I assumed it was probably to talk smack or something though I'm not really sure since no one said anything in all chat during the game, so I declined the invite. He seemed pretty intent because it would pop up every time I declined it. Lo and behold I got into the next champ select where he said "I'll teach you to unfriend me" and then proceeded to spam derogatory and racial slurs. As far as I know there's never been a feature to report someone for out of game conduct but I feel the behavior exemplified here is an extreme violation of social and digital conduct, so I was just wondering if there was any chance a rioter or someone could look into the chat logs from that champ select or something?