Green’s Dictionary of Slang

swag n.⁴

self-confidence, style.

[1946		Austin American-Statesman (TX) 7 Feb. 6/5: A number of Prussian officers came swagging towards us].
2014		C. Eble UNC-CH Campus Sl. Spring 2014 14: SWAG — swagger self-confidence, composure, style: ‘His outfit is swag.’ ‘Those players have so much swag—they get all the ladies.’.

In derivatives

swagless (adj.)

(US) lacking in self-confidence.

2012

Tampa Bay Times (St Petersburg, FL) 14 May C1/5: Let me apologize [for my] state of swagless being [...] From eavesdropping on kids via Twitter, swag is [...] style and attitude.