mad c
A mad c is someone who either does something so crazy it makes your head spin or something so boring it makes you want to scream. Either way, they're your best friend, so you're stuck with them.
You: "He jumped out of a plane with no parachute." Me: "That's a mad c."
You: "She tried to cook and set the house on fire." Me: "That's a mad c."
You: "He spent all his money on a pet rock." Me: "That's a mad c."