To steal someone else's unique style that sets them apart from the crowd, makes them famous, or otherwise steals their thunder making them warrant a lot less attention or swagger factor.
A good part popularized by celebs and hip hop songs like Black Eyed Peas - Boom Boom Pow. The female artists in the song sings, "Them Chickens jackin' my style. They try to copy my swagger. I'm on that next shit now."
A guy goes to a uppity club or a local trendy, upscale hang out spot with a few friends but dresses up in fancy black clothing to top the competition which earns him attention of beautiful women. He starts to notice more and more men doing the same looking and acting more like him. He realizes they are nothing but lame swagger jackers who have no real game of their own but to live off someone else's own success.
Lil Wayne is a Swagger Jacker, he copies B.I.G., 2Pac, Jay-Z (Jay-Z the most, and he had beef with him lol), His dad, and 2 other rappers, and even an R&B Singer! Best Rapper Alive my ass!
In basketball, when you take the momentum from the other team or player by crossing them up, making them fall, looking at them on the ground for a few seconds, and shooting the ball for three. It results in removing the swagger of the opposing team or player.