This is actually true for those who reading this and shaking your head in disbelief this is going on. I don't believe there is anyway to block his IP (the reason is the user is not connecting to your computer but the battle.net computer), but here is the teamliquid thread on it going on. According to them the only work around is this (edited for language)
To Play user map setting, make game name as desired but change gametype to Top vs bottom. Once your lobby is full.
Remake same game name with the password as "1" The reason is frux is just affecting the UMS (Use map settings) lobby list. A lobby list is just needed a name to bring them together.
For example: you wish to host lobby for sunken d. You would make the game name "Sunken D!!!" select the map but change setting in game creator to Top vs Bottom.
Now your game name is able to be joined. When your lobby is full, remake the same game name as before "Sunken D!!" just add a password you notify to use that in the lobby before you remake the game