A mental state where one covets the chair another is sitting in.
I had a hard time enjoying the concert. I was preoccupied with a bad case of chair envy. It seemed like everyone around me had chairs that looked like they were meant for human beings. That is the last time I buy a lawn chair from Walmart
-adj- One who desires to sit in the chair you have. Sometimes it's the last chair, sometimes it's not even your chair, but you long to sit down and be comfortable.
The people on the stairs looked over at us, and in their eyes we could see the chair envy.