How to tell your parents that you spent your money without them being mad?

alright so my dad gave me 50 bucks to watch my little brother.(i know alot) but i want to spend the fifty dollars on weed(yah i know i am stupid for smoking and all that ****) but how can i tell my parents i spent 50 dollars in one day if you could please help me.|||I would suggest you be totally frank, and admitted that you had been a complete ****, and blew their hard earned money. That way, you would no longer have that problem, as they would never give any you any more money. Simple!