1. Any made up phrase that makes zero sense.
2. An improved sentence to make as a joke, and possibly make yourself look stupid on purpose.
Wow, that muserism you said is so random.
Examples of Muserisms:
Elephants invented walking while juggling a pile of bricks.
The only way to get a splinter out of an elbow is to rub a gallon of peanut butter on it then slap it with a rotting fish.