From Longman Dictionary of Contemporary EnglishI should have thought ...I should have thought ...British English used as a polite or joking way of showing that you disagree with what someone has said or think it is silly ‘Why isn’t it working?’ ‘I should have thought it was obvious.’ → think
Examples from the Corpus
I should have thought ...• She's a pretty child, but hardly his intellectual level, I should have thought.• That is rather obvious, I should have thought.• The scent of the tea as I poured it ... I should have thought.• And marriage, I should have thought, is a false step you must have been well warned against.• This seems an odd argument for smoking to me and, I should have thought, to smokers, too.• It's very important to me - and, I should have thought, to you too.• The royal crest is used on the front of the annual report, which I should have thought was improper.• Any leader, I should have thought, would have demanded loyalty and support from a vice-president as a basic minimum. 