Play Dark Angels, and on turn four take all of your models, put them away, and say "Sorry, invaded the wrong planet. You know how it is."
Play with only bases. When your opponent claims to kill your Hive Tyrant, say that its a genestealer instead and that the Hive Tyrant has been at the front the whole game.
Anytime you successfully do ANYTHING, bend your arms and knees and lean back (ever so slightly) and shout, at the top of your lungs: "METAGAME? METAGAME!"
Play with an old Malal army. Claim you have Preferred Enemy and Furious Charge on anything Imperium or Chaos.
Whenever your opponent rolls a 1 to hit for any sort of high strength high initiative model, deep strikes off the table, or rolls no hits with a mob of shooting orks, do this:
http://www.youtube.com/watch?v=m0gVZm5QR_Q