Pastel-core
A genre of music containing bands whose t-shirts and other related artwork are characterized by bright, loud colors (pastel) and nonsensical designs. Usually worn by some skinny douche who thinks he's "brutal" or "hardcore" because of listening to said band(s). Generally just awful music but not always.
Example of bands that could be considered "Pastel-core" are Asking Alexandria, Suicide Silence, A Day to Remember, August Burns Red, etc.