The definition of either:
1) The Internet overinflating a trifle and milking it for every last ounce of content
2) Everyone and their gramma taking a current event and making a video about it
The word comes from the YouTuber W3TB who compares these actions to Hyenas ganging up on weak animals for food.
Pyrocynical was really ripped to shreds by The Internet Hyena's Grasp.