I.U.S (Involuntary uniform syndrome), either a one off occurance, or a constant accidental habit of wearing the same clothes as someone else.
Situation 1 - When explaining to a friend your dilemma
"I keep turning up places and making an IUS with people"
Situation 2 - When exclaiming to someone else in the same clothes
"Omg, we've got an IUS going on between us!"
Situation 3 - Two people walk in wearing exactly the same thing
"Wow, that's an amazing IUS!!"
Can also be A.U.S - Accidental Uniform Sydrome