From man + -tastic.
mantastic (comparative more mantastic, superlative most mantastic)
- (slang) Fantastically masculine or manly.
2005, Dan Levine, Avant-Guide Chicago: Insiders' Guide to Progressive Culture, Empire Press Media, →ISBN, page 123:Later, a mantastic crowd of foxy playboys and players lose their inhibitions (and more often then[sic] not, their shirts) shaking it to high energy dance tunes.
2007, Candy Halliday, Dinner First, Me Later?[1], Warner Forever, →ISBN:Mantastic as Jake was, one thing was certain.
2015, Devon Hartford, Painless[2], →ISBN:Romeo batted his eyelashes at Crew Cut and said, “Mmm, aren't you mantastic.”