1. Feeling fantastic after the successful completion of a particularly macho feat.
2. The act of completing a stereotypically macho feat.
3. Often used snarkily in battle, i.e:
"dude, your ex-girlfriend is a lesbian now?"
"fuck you, your the one wearing the mantastic earings."
4. Term used to describe a person radiating testosterone.
Pirates are mantastic because they get two types of booty.