There seem to be several suggestions: the most common is that comes from being unemployed, but there seem to be some gaps in the chain, then there's rhyming from "Mad as a March Hare", and from "spare tyre" as you say.Marcus Aurelius wrote: ↑15 Sep 2021, 11:13pmThe origin of to go spare, as in get angry, derives from the Cockney rhyming slang ‘spare tyre’ meaning to show your ire, by extension to get irate.
https://english.stackexchange.com/quest ... -get-angry
https://english.stackexchange.com/quest ... e-me-spare
http://www.word-detective.com/2009/04/d ... -go-spare/
Jonathan