"When I was in Vegas, I was just there chilling in my room, me and Eleanor [his girlfriend]...the door knocks. I would normally look through, but I didn't," Louis Tomlinson told us of his craziest fan experience.
"So I open the door, just in me boxers, I think...and there was this girl there and she just stood there shaking and crying!" he explained. "I was like, 'Whoa! What's going on, love?' I closed the door and ran away!"
Harry Styles said one fan pushed their security guard, while Niall Horan got knocked over by an overeager Directioner who jumped on his back to try and get a photo.
Hit the clip to hear the This Is Us stars spill on the best and worst parts of being world famous and what celebrity they were most excited to find out liked their music.
See more of the 1D boys on the big screen when their movie hits theaters this Friday, August 30!
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Gallery | One Direction: 'This Is Us' World Premiere!