Can I report someone after I start a new game?

I was having a rough go at Sion top. I ended up not bringing Flash, so I got camped top. Which I expected, it's my fault for not bringing Flash. What I didn't expect was the Urgot/Volibear combo top diving me under tower and tossing me back and forth. Naturally, I got stomped, and the Urgot was trash talking. Nothing too bad, just some normal japes. I decided I learned my lesson.

The Urgot friended me after the game. He was relatively friendly in game so I said yes.

Then proceeded to wait for me to get into game and flamed me, saying I was the worst laner he'd ever fought and that I'm fucking trash and that he hated me for being bad, after he already stomped me. He proceeded to swear and insult me, only to immediately unfriend me after he was done so I couldn't respond. Is there a way to report someone like that after our game has already expired?