Neglecting their litter box
Yes, for us humans, it's annoying. It's normal that after a long day, when you finally get home from work, the last thing you want to do is clean up the little gifts your cat has left in their litter box.
However, for your cat this is very important. Having a dirty litter box is not only uncomfortable for them, but it makes them feel neglected, self-conscious, and vulnerable. Even if they don't relate this offense directly to you, you could suffer the consequences all the same: your cat might choose instead to start doing their business on the carpet, in the closet, or in a corner, rather than using a litter box that's filthy or smells bad.
So when you're feeling tempted to just leave the litter box till the weekend, just think about how you would feel if you only flushed the toilet on Saturdays...