An Earworm

That's right, bitches. You better hide!

An earworm, according to an expert formerly called Minty, is a tiny legless arthropod that gains access to the chochlea via the lobe and entrenches itself in the flesh. The only way to dislodge this parasite is by introducing another, perhaps more pleasant earworm into the same area.
An earworm is also a phrase from a song that enters your mind and just keeps spinning in there over and over again all day until it makes you sick. It can also make the people around you sick  if you find yourself absentmindedly humming  it out loud.
The only way to stop it is to start another one. Perhaps from a better song. Otherwise you could be stuck with freaking Party Rock the whole day.
The vicious thing about earworms is that they are no respecters of taste. You can be struck with one from a song you completely and utterly despise. In fact, this is most often the case, as the quality that makes a potent earworm is the same quality that makes a successful pop song: a repetitive, catchy phrase.
What triggers off an earworm? How does one get infected? It mostly starts when  you are walking around, minding your own business, and someone mentions the song, or even just says, at random, a phrase that is in a song. For example, the following passage is toxic with earworms.
Party Rock is in the house tonight, so grab somebody sexy and tell them hey. But if theres a sky full of lighters you are not a golddigger so I’ll give you my heart, I’ll give you my soul, I’ll give you my goodies. Locomotive’s taking over now (choo choo choo choo) so get Alejandro on the video phone because toli Superman.

I am sure I just destroyed your inner ear.