Beyond vocal tonality and the way they carry themselves, there’s another easy way to tell if someone will be an interesting person. When you meet someone new, simply ask them, “What are you passionate about?”
90% of people will say, “You know… I like to eat, or ummm watch football, uhhh hang out with friends.”
Beyond simply having generic hobbies (which isn’t always a problem in itself), these people are also likely to respond to you in an uninspired fashion. They’ll also often hesitate before responding. If the response you get from someone is similar to this… they’re almost guaranteed to be uninteresting.
If someone can’t be engaged and energetic when talking about something they love… it’s likely any further conversation with them will prove to be dull as well.