Someone randomly trolled my game

I was playing with my friend everything was fine we found game accepted and we were on champion select everyone called their lanes and picked except one platinum ( diamond last season ) It is incredible how this matchmaking works I once even played against Challenger at Flex on mid the problem is I was at level 27. Anyway this guy said Im gonna troll and int and I replied with just “ok” because If I had said something else like “don’t” he would surely do it anyway. The game started and he came to my lane saying he will troll me because I said “ok” and Yes, he did troll and we lost game.