A raptor apocolypse is an apocolypse with raptors in it. It usually happens when some scientist replicates the DNA from a mosquito trapped in amber.
Scientist now: Hey, lets take this dead mosquito and get the blood from it so we can replicate dinosaurs...it will be awesome!
Scientist next week: OH MY GOSH! KILL IT KILL IT! ITS A RAPTOR APOCALYPSE!