He was giving me the bum shoulder

This was uttered in haste, as most malaphors are. It is a conflation of “give the cold shoulder” (to snub someone) and “bum rap” (an unfair accusation or punishment). Both are negative actions by someone to someone else. “Give someone the bum’s rush” might also me in the mix, as this is not only snubbing someone but actually forcing someone to leave. A big thanks to Susan Ivison for hearing this one and sending it in!

Regarding the idiom “to give/show the cold shoulder”, the term dates from the early nineteenth century. It was frequently used by Sir Walter Scott and believed to come from the custom of serving hot meat to welcome guests, and of serving a cold shoulder of mutton or beef, considered a much inferior dish, when they had outstayed their welcome.