I heard the weather report about a cold front coming in, so I'm going to tell my little brother to wear shorts.
Dude, why are you picking on your little brother? You want him to freeze his ass off?
It'll be hilarious to see him shivering in the snow!
You are a terrible brother for neither looking out for him nor making sure to keep him safe. You should be telling him or anyone else in your family to dress appropriately for the cold weather approaching.
I'm going to tell my mom she should wear two shirts.
Well, at least you're not going to trick your mom, too. I hope your little brother doesn't get frostbite or catch pneumonia running around it the cold weather. It's OK to play jokes on little brothers, but not when it could jeopardize their health.