Sheremetyevo International (SVO), Russia
This airport isn’t dirty, overcrowded, or lacking in seating. But it is outdated, bleak, and greatly overshadowed by the nearby Domodedovo International which has a much better reputation.
It’s also famed for the awful customer service. The terminals and airport are miles apart which makes transfers a real pain, and flights are frequently delayed. Broken signs are another common feature. So it’s still terrible.. just in its own special way.