In case something happens to that thread:
1) Open console.
2) Type "voice_show_mute".
3) Find nickname of the person you want to mute.
4) Remember this person's ID.
5) Type "voice_mute X", X is ID of the person.
* This only mutes voice. Text chat messages aren't blocked.
* To unmute the person, type "voice_unmute X".
* If you want to mute voice chat entirely, type "voice_enable 0". This will mute your voice too, noone will hear you. If you want to unmute voice chat, type "voice_enable 1" and restart the game.
* If you can't open you console (by clicking ~ key next to "1" key), go Options -> Keyboard and mouse -> Activate developer console.