We are aware of a possible issue where the game may become unresponsive if a player is wearing the "MY EARS ARE RINGING" Psycho head in a multiplayer game.
We have identified a solution and will be coming to PC, PlayStation 3, and Xbox 360 in a future update.
In the meantime, we recommend not using this head with players who do not own the Tiny Tina's Assault on Dragon's Keep.
Keep an eye on our Knowledge Base (http://support.gearboxsoftware.com/forums) for any additional details moving forward.