I think it's loading the dishwasher in our house. Sometimes I feel like a dang wizard when it comes to how efficiently I can load the thing. She just throws dishes in there, and wastes about 50% of the space. So I rearrange it, and add more dishes. I think it drives her nuts.
ETA: We actually work quite well in the kitchen, and enjoy preparing meals, etc. together. The problem is being motivated enough on the weekends to prepare meals in advance so we don't have to worry about it in the evenings after we get home from work.