I dunno. “Are you busy?” sounds open ended and is a bit presumptive (I don’t know you, what business is it of yours?). Do you have a second seems more casual and nonchalant without being particularly rude while succinctly indicating you aren’t asking for lengthy or in depth attention. You’re playing on a natural tendency many people have for simple charity, and then once you’re in… well, lots of us have felt trapped in unwanted situations because of a fear of being rude, right?