Mine would be death, that scares me the most.
Then it would be maggots or cockroaches or summit.
But what i don't get is, you would know it isn't real. Like when Hermione faced a boggart, come on! She's a brainy kid, she should know that it isn't real. If my biggest fear was failing, and the boggart turned into someone telling me i'd failed everything, i would laugh.
*is afraid of like 50 million things* either a clown, needle, or spiders...I was watching a movie that I didnt know was going to have 50 million spiders crawling all over the place but of course it did and my friend was over and Im like gah *squeak* and shes like cute ron face...it was kind of akward