Selective Dishwashing
Every time my roommate cooked with her boyfriend, which was almost nightly, she left a pile of dishes in the sink. So, naturally, within two days the sink was overflowing and there were no dishes or utensils to eat with. We had a dishwasher, which made this way more infuriating.
Anyway, one day I had completely had it when I saw little bugs flying around the kitchen. I told her she needed to do the dishes immediately and left for work. When I came back, the dishes were in fact done. However, she had left behind the one single knife I had used that morning, dirty in the sink.
Even after I had washed and cleaned up after her for months. The level of petty was astounding to me and, honestly, I think about that incident often. Story credit: Reddit / WiFi_for_dogs