It was only four months ago that I was sat in a pub at lunch time with my head in my hands. —Nichola at Looking Glass Society She called back to me, from where she was stood up at the front of the queue, she said, 'Where was it that Morrissey lost his bag?' —The Wrong Boy by Willy RussellTo Americans, this passive use of the verbs sit and stand sounds strange. Interestingly, you don't get the same passive usage for lie so much, with either the (usually intransitive form) lain or the (usually—or at least prescriptively—transitive) form laid. Better Half (who's ok with passive sat) says he wouldn't say this at all--but some (like Rebecca in the comments!) would. Here are some web examples:
Anoron sat in a plush chair within Legolas' room. He was lain on the bed; sheets slewn about him, his bare beautiful body showing as he lay on his side fast asleep. —from what appears to be Middle Earth slash fiction by Anorista His nose was bleeding and he was laid on the bed face down. —The Daily Mail
Today I was struck by another use of passive sat in the documentation for an examination board, which said something like:
The exam was sat on the 29th.In AmE, one takes exams rather than sitting exams, as they do in BrE. Since sit in this instance is transitive, with exam as its direct object, it's perfectly grammatical in the passive in BrE.
Students sit exams or write them in BrE, and examiners set exam papers. But in my first teaching job outside the US, I frequently said I have to go write my exams, confusing my colleagues who thought I already had the requisite degrees. I now set papers with the best of 'em. Unfortunately, this means that I have to (BrE) mark/(AmE) grade them too.
Outside the US, I also had to learn to invigilate exams. The first time I heard this term, I said to my South African colleague "Oooh, that sound painful." He said, "Well what do you call it then?" "Proctoring", I said. You can imagine his response.