When you're going to Titanic: It's the best ship in the world.
When you know it's sinking: It's the poor ship!
Titanic's Reputation
Explanation
Explain Bear
Okay, so basically, the joke is about how people's opinions change when something bad happens. Like, when the Titanic was setting sail, everyone was all like, "OMG, this is the best ship ever!" But then, when it started sinking, they were all like, "OMG, this is the worst ship ever!" You're probably like those guys who change their minds all the time. You're fickle.