Neighbor complained about me walking at midnight, what can I do about it?

A guy who moved into the semi-basement apartment a few months ago has been complaining to my landlord about me walking too loudly after midnight. I don’t stomp or make excessive noise—I just go to the bathroom a few times before bed, and that’s about it. He’s driving me crazy because he complains about everything—saying I shower too late, walk too loudly, etc. After my landlord first mentioned his complaints, I made an effort to walk more quietly and even asked my mom to do the same. But she’s an elderly woman—she can’t just tiptoe around the house. It’s ridiculous. Why doesn’t he just buy some earplugs?

What can I do with this situation? He is not even an old man, he is like a twenty something man. I've never had a neighbor who was so fussy about a couple of steps.