Green’s Dictionary of Slang

pants adj.

[pants n. (1)]

rubbish, second-rate, inferior.

Online Sl. Dict. [Internet] pants adj 1. inadequate, displeasing, or of poor quality. Possible origin: underwear, called pants in Britain.
[UK]S. Kelman Pigeon English 73: My trainers are called Sports [...] Everybody calls them pants but they’re just vexed.