Merde! (or, if you're slightly more calm, Mon Dieux (sp?)(Or, apparently, Sacre Bleu, although I've no idea if this is accurate or just someone's idea of what French people exclaim.)

In German, I'd imagine there's all kinds of things you could say. German is a great language to swear in, since even saying something as innocuous as "Would you like some tea?" comes out sounding like you want their mother butchered by crazy gophers and staked out for the rest of the summer.