This achievement will require a minimum of 9 people to complete,
Once you and your 8 friends are together start a server on the map "Pass_Brickyard" once the map loads you will need to split into each team using the list below.
Red Pyro
Red Sniper
Red Soldier
Red Medic
Red Heavy
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Blu Scout
Blu Demoman
Blu Engineer
Blu Spy
At this point you will need one player to stand by the guitar shown in the image below and then have some one else go to the same spot but on the opposite side once there shoot the guitar and a door marked "Private" in each spawn will open showing a teleporter.
http://imgur.com/QatvWigOnce inside of the room shoot the cord off the back of the t.v and have your friends stand in specific points in the room as show below, when every one is in the correct position the achievement will unlock.
http://images.akamai.steamusercontent.com/ugc/49577679735760...This will grant the Military Grade JACK Hat & PASS Time Miniature Half JACK