I dare Merida to colour Jack's eyebrows with a skin-coloured paint and tell him that she shaved his eyebrows off.
Merida: -laughs evilly and cackles-
Jack: What's wrong with you? Who laughs like that?!
Merida: Oh nothing i just thought of something weird.
Jack: Yeah with that brain of yours, i wouldn't even want to know what you're thinking. It's getting kinda late. I'm going to sleep first. Have fun with...whatever you're thinking...
Merida: ...oh i will...
-While Jack's sleeping, our devious protagonist Merida goes to the bedroom-
Merida: NYEHEHEHEHE -paints on Jack-
Jack: Ughhhh....weird...-snores-
-The next day...-
Jack: That was one hell of a dream...i dreamt that someone shaved my eyebrows off...
Merida: Oh my golly Jack! Your eyebrows!!!They're...GONE!
Jack: WHAT?!MY BEAUTIFUL EYEBROWS ARE GONE?! OH HOW DID IT HAPPEN?!
Merida: April Fools!!!
Jack: What? Oh come on, it's not even April Fools Day. You gotta be kidding me!
Merida: Every day is April Fools' Day...for us at least.