Quote Originally Posted by Fiery Diamond View Post
Someone else already addressed the buttload//boatload issue below, but I wanted to respond about the other one.

It's just that single phrase that's like that, not all cases of "another thing." Here's what the phrase means:

If you think [X]*, then you've got another think coming.**
*If you think [X]
*which you clearly do, or I wouldn't be saying this
*which is also NOT the way things are going to be
**then circumstances/my actions/events/etc. are going to force you to rethink ("another think") and change what you think because you're wrong

Link
Another way of putting it is "Your think is defective. I will replace your think for you."