Yank is a term used by those who don't know what it means.
Not necessarily. I get called 'yank' by my ice hockey teammates all the time and , technically, they're not 'wrong' as such and many of them even know why! The state of my birth was a union state, hence those with
"a long southern drawl" might describe it as a 'Yankee State' (some down there really can't let it go).
SPAM is an acronym, and is indeed offensive, once one understands what the letters stand for. Who in their right mind is OK with being called a Motherf*cker?
SPAM is a portmanteau of 'SPiced hAM', and is a term used to describe us that came about from food sent to the UK during WW2 from the US which included the ubiquitous tins of SPAM. Any crude acronym that later came about is an aside and moot. I'm quite proud of the term 'SPAM', its a little reminder everytime a Brit says it that the US helped save them from starvation.