Green’s Dictionary of Slang

rubbish, second-rate, inferior.

1997–2001		Online Sl. Dict. 🌐 pants adj 1. inadequate, displeasing, or of poor quality. Possible origin: underwear, called pants in Britain.
2011		S. Kelman Pigeon English 73: My trainers are called Sports [...] Everybody calls them pants but they’re just vexed.
2020		Twitter 2 Aug. 🌐 The last few months have been a bit pants [...] but this week is going to be one of celebration and comfort, starting...now.