Plane etiquette: keep your seatbelt fastened unless it is safe to walk around the cabin. Turn off all mobile devices until a flight attendant tells you it is safe to operate your electronics. Do not taking photos of a sleeping Niall Horan.

The One Direction superstar was aboard a flight when his evidently eager seatmate decided to strike up conversation. And, as he was more than dismayed to learn, his newfound plane-friend decided to invade his privacy with a sneaky snap while he was sleeping — against his wishes.

"To sum up the PERFECT European adventure, I sat directly next to Niall from One Direction for 9 hours on my flight home from London last night," the giddy fan wrote in a caption accompanying the photo of a sleeping Niall. "He was sick and asked for no selfies, but here is a pic I snapped when he was sleeping lol he was so friendly! Talked about Ireland, LSE, lolla, and more. Not a British Duke... But an Irish Popstar will do ;) thanks for treating me so well Europe!"

Uh, you're welcome? In any case, Niall wasn't having it.

"I think this s--t is unreal. I mean if you can't sleep on a plane without people taking photos of you,what can u do," Niall wrote on Twitter along with the photo. We agree — a rude move, especially considering he was sick and requested no photos, but still nice enough to hold conversation.

Invasion of plane privacy aside, the singer seems to be doing well: he was recently spotted in public holding hands, hugging and kissing his rumored new girlfriend, Celine, at the British Summertime Festival in Hyde Park.

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