In the newest Overwatch PC patch,the “Avoid This Player” function was removed. It seems to have caused problems with the matchmaking system, so Blizzard decided to get rid of it. The “Prefer This Player” function will remain in the game, though.
“The ‘Prefer’/’Avoid’ player system was designed with the best intentions; however, it’s not currently performing in a way that we feel is healthy for the game. While the ‘Prefer This Player’ option is more or less working as intended (and is thus still enabled), the ‘Avoid This Player’ option has impacted the matchmaker in a negative way and led to some very poor player experiences. Although we like the idea of being able to say ‘hey, I’d prefer not play with this player’ the implementation of this mechanic is not where it needs to be, so we’ve disabled it and will be removing the UI option in a future patch.”
Overwatch is currently available for PC, PS4, and Xbox One.