The problem with this line of thinking is that everyone is selfish and inconsiderate sometimes. Everyone. EVERYONE.
Assuming you have a SO, you've probably been somehow selfish or inconsiderate towards them in, say, the last 48 hours. You may not even realize it. It happens. We're people. We are inherently selfish and inconsiderate. Just be around young children for like ... 10 minutes. Tiny little Hitlers. Every single one. Because they haven't been taught to suppress that part of themselves in public yet. They haven't figured out that other people exist and have value.
So when you treat your relationship like some competition between who can be less (or more) inconsiderate and selfish, are making tallies in some mental list of perceived slights, are assuming your SO is just being a dick when they ask for a simple favor, are expecting them to explain themselves every time they say or do some trivial thing you don't personally agree with ... when you do that, you are being a child. You don't trust your SO. You value yourself more than them. And you shouldn't be in that relationship anymore.
But that's like way, way, way, way, way down the line from holding her purse.