swagtastic is when you have amazing game (swag
Swagtastic derives from the words swagger+fantastic, so literally swagtastic means having fantastic swagger.
swagtastic is used as adjective describing a person and/or his game or ability to get girls
"Yo i can't help it my game is jus naturally swagtastic, my dude"
"Yo he wuz pimpin da other night, his game wuz lookin mad swagtastic"