hmmm... pet peeves...
How about 127 A$Cxxxxxxx blocks in every client file you open, seems they're part of his border drawing. An empty drawing with nothing but the border is 400K.
or
Exploded DIMENSIONS
Elements with Color, Lineweight, or Linetype set to something other than BYLAYER.
Almost, but not quite, on coordinate.
Multiple copies of the same drawing scattered all over the network.
Drawing names like "BUBBA03"