well, what your friend is doing is kinda of a d*ck move, but from what i understand of the ban system it shouldn't matter so long as the people he is reporting aren't falsely being reported by multiple people for several games in a row.
The way I understand it is that a player is only flagged if multiple people in the same game report the same player. Then only if the player being flagged is flagged multiple times within a certain number of games is that player punished. The way the system is set up false reports shouldn't have an effect, but i'm sure there is at least one player who has somehow been punished unfairly this way.
Unfortunately riot had to implement an automatic system because there are simply too many reports for their staff to handle and that does create the possibility for unfair punishments, but Riot did put some thought into the system to minimize this threat. The best we can do is restrain ourselves and not ban out of a salty attitude, and hope others do the same.