My first thoughts when I ship a couple of characters:
"Hey, they'd be nice together."
And that's pretty much all it takes. If you've ever done this, you've shipped. The insane dedication and online arguments are just the deep end of that, but not necessary. Obviously an interest in romance leads one to discuss it with others with the same interest, thus these threads. If you don't get it, you just don't have any interest, which is fine.