Reporting players outside of post game lobby.

I'm trying to climb solo/duo Q and it's really frustrating when people think it's ok to steal roles. obviously the player who is supposed to have "top" for example gets the short end of the stick when the support asks in lobby if he can play "top" when the answer is no. Thats all it should be, Instead our support auto locks Garen(the guy has a 30% winrate with 160 games on Garen...) and tells our actual top lane thanks! pick a CC support. Now we have a totally unfunctional team comp and my options are play this game for 20 minutes knowing everyone will rage at each other of I can dodge and suffer the point loss. There has to be a better way Riot! This guy should be reported for stealing roles, failure to communicate, and unsportsmanlike conduct, instead I bite the bullet and suffer the LP loss and wait time(ok its like -3 lp and 5 minutes really not a big deal) but how is this fair?