bench warmer —(coll.) a substitute in a sports team who seldom plays:
- He thought about leaving after the 1994 season, his third straight year as a bench-warmer.
chair warmer—(coll.) 1. (derog.) an ineffective office holder or employee:
- The judge frowned at me. The courtroom chair warmers craned necks in my direction.
2. (pejor.) a person who lounges for long periods sitting in a chair:
- He never takes me out anywhere. He’s a chair-warmer at home for fair.
See also: keep the seat warm / warm the bench.