Over at the PD Forums, we were having a discussion about how to create discord within someone’s environment without ruining their day. Nigel had this advice:

Extremely subtle, confusing changes; funny. Extremely large, confusing changes; possibly funny, if done with a high level of forethought. I like to plant products in people’s houses, and do shit like replace their half-used jug of milk with a half-used jug of different milk, or put a handful of mayonnaise packets in their butter compartment, just because it’s subtle enough to make them question their own realities. Adding magazines to their bedside table or stuffing a pair of socks under the blanket at the foot of the bed, or adding a pair of shoes in their size to their closet, are also good. You can choose things which really DO fuck with people’s MINDS, making it a MINDfuck and not just an irritating obvious prank.

from the GASM Command forum.