So when Fallon posed various spoilery questions, with Harington instructed to answer yes or no with a wink or a blink, well, you get it.
That means that when they're out they always have it shouted at them.
While on The Tonight Show starring Jimmy Fallon, Harington discussed his Saturday Night Live hosting gig, as well as constantly getting an iconic line screamed at him on the street. "My brother managed to get it into the end of my best man's speech", he shared. But even Harington had to imagine it was "quite sweet, actually". "He said 'Looking at the woman you're marrying, it shows you do know something, Jon Snow.' Which is sweet".
Kit posed on the red carpet with his spouse and former co-star, Rose Leslie, where Emilia Clarke was also in attendance.
Speaking of Harington and Leslie's relationship, Fallon also asked him if it was true that he once attended a costume party dressed as Jon Snow. On top of that, it was for his wife's 30th birthday party. "It's really bad taste".
The problem was that not everyone they'd hired to work the party knew the theme of it.More news: Man charged with making false statements after abuse claim
At the premiere, Kit and Rose revealed they were "tethered" by Game of Thrones, having met back in 2011 whilst filming season two. "It's like, 'You sad, sad man'".
This time around, Fallon and Harington set up the gag with all the subtlety of a rampaging White Walker, belaboring a set-up that explained how Harington's inability to wink resulted in a facial tic that fell somewhere between a wink and a blink.
There was just one problem.
One thing we do know absolutely is that Harington is really going to miss portraying the King in the North. The Jon Snow actor is forced to enact her version of Game of Thrones, calling it "Game of Jones".
The first episode of the eighth season of Game of Thrones lands on HBO on Sunday 14 April for viewers in the United States, while the UK can get their fix in the early hours of Monday 15 April.