Iroh crushes are the result of the fact that Iroh is an old man. If you're nice to him, he'll give you tea. If you're mean to him, he'll still give you tea.

And if you get in his way, he'll firebend your ass from the Air Temples to Ba Sing Se.

Then he'll give you tea.

No matter what, you're going to get tea. And you better like it.