This is a good example of a word in popular culture which has changed in meaning. Usually what happens is a word is adopted by a fringe culture, and then eventually it makes its way to popular culture and everyone uses it- but by then the meaning has changed to something milder that what it originally meant. A 'trip' means a drug trip, a psychedelic experience, which may be strange or puzzling. I think the closest analogy is when you take a boat ride- you get on the boat and float somewhere, good or bad, and when you are on the trip you can't get off the boat until the ride is over, whether you like it or not. But then the term changed to also mean when someone is very stuck in their point of view- "oh, that's just their trip" -because it means something which only that person is experiencing, the people around are not. Like someone who is worried about something that nobody else is. So to say about someone 'She's a trip" or "He's a trip" or about something "it's a trip" means that it's strange,a nd that may be a good thing or a bad thing. Either way, it means something strange and intense and possibly difficult to deal with. Frankly, I hear people say this expression about someone as a way of avoiding saying much worse. For instance: "I've met his roommate. The guy's a trip." (raises eyebrows and sighs) And maybe the truth would really be: "I've met his roommate, all he does is talk about politics and he likes to get mad at you. I'd rather not talk to him." So to say something is a trip means either it's really strange and wild, or else it's challenging but the speaker doesn't want to directly say why.