I solo queued and found myself in a party with a coach who insulted and harassed me during the match. There was no way I could find to mute or report him; in fact he laughed about how I couldn't mute him because he was a coach, so I suspect this is a loophole he regularly abuses.

Match 2872445457

Offending coach: http://steamcommunity.com/profiles/76561198174008298