Oh sure there are lots of people free-associating on the meaning of it, there are even stories in the well tread pages of QST and other amateur radio scandal rags. Much ink, and whatever the internet is made of, (puppy blood for the record) has been spilled on this topic.
According to me, here are the candidates:
- Ham it up, jerkface! -- This is an old-timey way of saying talk to random people about nothing in a jovial manner. You see this around periodically, with Mr. G. West being the prime offender. I can say with some authority that this is not the correct answer.
- Hamateur radio operator -- My personal favorite, but only useful for trolling
- Ham handed -- Maybe this refers to the morse code straight key
- Someone just likes pork products -- I'm going to chalk this up as the most likely answer.