1. The combination of the words thrash and fantastic, often used while discussing metal. This is not limited to metal, however. In order for a song to be thrashtastic, it must be fast-paced, contain some nasty riffs, or having powerful drums.
2. A word that indicates an exciting event that is taking/has taken place. This includes, but is not limited to: Parties, concerts, road trips, eating sushi, having sex, watching college basketball (or any other exciting sport), and fistfights.
1. Have you listened to this guitar solo? It is thrashtastic!
2. Hot damn; my girlfriend was absolutely thrashtastic last night.