Atra du evarinya ono varda.
I'm a little worried because I got it in GTS, and I've hatched like 5 other, newer eggs and this one still isn't even twitching.
Just be patient and ride your bicycle up and down a long stretch of path such as the Cycling Road for generations that have them or the Skyarrow Bridge in B/W or B/W2. It might take a little while more, but that egg will hatch sooner or later. The possible number of steps for an egg might vary from 5000+ up to 10,000 maximum, but don't worry about this and just keep on riding. Consider doing something else at the same time while riding back and forth as this activity might get a little boring.