The art of exercising caution while frightened out of one's wits.
If you're going down to the old boathouse armed only with a torch at this time of night to investigate the strange goings-on, unexplained disappearances, and terrifying noises, then just make sure you're scareful.
A mixture of caution and fear, usually associated with doing something you are not supposed to be doing.
Ashley: You driving home with all that weed in your car?
Ashley: Be scareful.
Me: Oh I will.
Aaron: He drove home drunk?
Me: He'll make it he's going to be scareful.