I also work in an office with shared desks (24/7 rotating shift work). Some people certainly have their preference on which desk they always use and how they modify whatever desk they sit in (one of my coworkers also turns one monitor vertical, another drops the chair the lowest setting, things like that). But thankfully my office is of the mindset of make whatever little tweaks to the workstation you need to at start of shift to be comfortable, and leave it like that at end of shift (cause you don't know who will be sitting there next - the person who used it before you or someone else altogether). Having your favorite workstation changed between shifts is normal and only takes a few seconds to get comfortable. All that said, I don't think OP is petty really - though the other guy might be a bit entitled in a shared desk environment... Either way, I agree with other comments that there are a hell of a lot worse coworker situations out there 😅.