Think of any SC hack out there that employs a host hack. Now think of a bot that can also join SC games.

Add this two and you could have a bot that could look for a specific user or game type and prevent a game from happening. Imagine the possibilities...Force a particular user to host private games or deny any games for a specific genre.

Think you are having a bad day? Load 8 (I think 8 will cover it) bots like this and take down all games on a server.

I wonder if something like that exists. Could it force a patch maybe? Anyways, just an idea I had.

It might be possible, haven't looked into that throughly though.  Apart from the initial Command 0 packets mostly, the rest are asynchronous, so you can really get a bunch of different udp packets at anytime, based on whatever needs to be resent or whatever to keep the sequence count aligned. Which is why SC UDP is such a mess and sort of confusing at times to deal with. 
But you could join the game and keep requesting certain packets to be sent your way by host, and keep requesting them, so that you never really join the game but at the same time in you're still in it.  Which basically makes you invisible while still being able to see everyone in the room and see their chat. 
Theres a bunch of ways to mess stuff up in SC udp that I'm sure would cause problems for starting a game. 
Good idea though , evil indeed

You could do exactly what a host hack does and use SNetDropPlayer on the host. You also don't need to send packets to Battle.net to join a player's game in order drop them(avoid flooding Battle.net). You could effectively prevent every public game from remaining in the games list for more than 5 seconds.