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 Precedent (rooted, AreaRom 3.4 , sd-ext w/ 3.65GB internal space)
Kindle Fire (1st Gen, rooted, AOKP JB 4.1, Nova Launcher)
Samsung Galaxy SIII 4G LTE (rooted, Carbon ROM)