Stealing somebody else's ways, copying their swagger. Popularized by Juelz Santana.
Newer rappers are always swagger jacking artists like Tupac and B.I.G
A person who jacks or steals someone else's swagger. When someone that is not very cool takes feels the need to take someone else's swagger or awesomeness.
Raul: Oh my god I'm so awesome! And i think I'll take the Spanish name Cristobal!
Josh: Oh my god that Raul kid is sooooo awesome and cool! The only way I can be as cool as him is to Swagger Jack him and take the name Raul.
Raul: Stop Swagger Jacking me, you will never be as awesome or cool as me.