How do I tell my parents I lost something important?

I know I'm not responsible. I managed to lose my military ID card. It probably wouldn't be that big of a deal, if I hadn't lost my ID card on several occasions in the past. My father has severe bipolar disorder (recently, my mom wouldn't leave his bedroom, and he punched a hole in the carpeted floor, and broke several bones in his hand), and my mom is foreign, and essentially bases the proper reaction to any situation by my father's reaction. Consequently, it's imperative that I break the news in the best way possible. I don't really care if I have to lie to them, as in telling them someone stole my wallet out of my backpack or something, but it's very imperative that I tell them I lost my ID, because I would like to recieve some medical treatment, and can't do so until I have my ID. If at all possible, I need to know an exact how, and when to break the news in a way you think would cause the smallest reaction.