Long, nasty notes on dirty dishes in the sink, silent wars in the work break room, tapping the ceiling with a broomstick on your loud neighbors, or doing pretty much anything to avoid an actual conflict or confrontation is "passive aggressive" territory. While it can be definitely be a funny technique to let someone know you don't approve of their behavior (shout out to the roommates who put people's dirty dishes on their beds) it's not always the most efficient approach. More often than not passive aggressive just makes everyone even angrier, escalating the original problem into a silent treatment in person, but delightfully mean email chain territory.
So, when a Reddit user asked, "What is the most passive-aggressive thing you've seen someone do?" people were definitely ready to share the craziest, pettiest acts of non-confrontation combat they've seen go down.