Honestly, I kind of wish I could. But my second language is Italian, which isn't exactly exotic, and both cities I've lived in have had enormous Italian communities, so it's never been safe to assume that nobody within earshot would understand. I just figure that, wherever I am, there's at least one person who speaks enough Italian to be offended. =) And, in the end, I do feel like it's rude to use a language that not everybody in the conversation can understand. I'd be insulted, so I don't do it. Besides, I generally use Italian when it's the common language of everyone I'm with. There are definitely times, though, when I wish I could speak Swahili, or another language that's less common than Italian. =)