Being deemed "Swag Master D" (Which is now my steam name) for my ability that I have two girls pursue me at the same time, I shall try and give a description.
Swag is assured confidence that is evident, whether through appearance or through one's actions. Given the circumstances, this can give an air of being badass. This can be done by being unfazed, stoic, professional, and having things under-control.
Swag can attract members of the opposite sex if they favor such actions.
It is the lesser version of class, with class being the more gentlemanly and holding a greater standard of etiquette, whether it be respectful or a honourable.