1)To toss ideas around with no expectation of them coming
to pass, to brainstorm.
2) To make harmless jibes or attacks; make weak accusations.
1)We were spitballing about the upcoming election.
2)I was just spitballing him, but he took it seriously.
To make a suggestion loosely, often one that goes against common logic.
"Now I'm just spitballing here, but why don't we pay off our loan in Canadian dollars and save ourselves soem money?"