The unmovable object and the unstoppable force

During the conversation I began about below this very post, I somehow managed to amuse both Honeydew6692 and Joshli88 at the same time without even thinking about it twice. (Thank you, thank you.... by the way, Honeydew6692, once again...... feel better. Seriously. Just feel better already. Come on, you can do it.... UGH! Fine, be that way. Go ahead, cough or something. Neh.)
Anyway, Joshli88 was telling me about a class discussion he had during school about what would happen if the unstoppable force and the unmovable object collided. (If that's hard to imagine, think about what would happen if a tank ran into a minor hurricane.... Ya.) "And so," he concluded, "The most popular idea was that if the two collided the unstoppable force would become the unmovable object and the unmovable object would become the unstoppable force. Since they can't exist together, the would become one another."
"Since they can't exist together, they become one another...." I muttered. (I tend to do that a lot.)
Without knowing it, I was making a connection.
"Oh! Just like what happens in Freaky Friday!!!!"
Joshli88 immediately burst into laughter, and Honeydew6692 said that if she laughed she'd just end up coughing. (I TOLD YOU TO GET BETTER!!!!!!!!) I hate to admit this, but I didn't understand immediately what they were entertained by, like I should have.
It took me a few moments to register.