the one time I remember hearing the term 'Planet X' was the odd visual reference in one of those old Marvin the Martian episodes, where he was setting up his camp on planet 'X' which was literally shaped like an 'X'
the new term, 'Nibiru' sounds more like an Anime character to me
Samsung Galaxy S4 **NEW** (GS3 screen finally shattered)
Samsung Galaxy Tab 3 7.0 (non-rooted, stock)
Samsung Galaxy Tab 2 10.1 (obsolete, slow, rooted)
Samsung Galaxy Note 10.1 2014 Edition