Beaten Assen is half spanish half english. It means you are going to or already have beat someone up, killed them, or t-bagged someone.
Black Guy: Yo my niggy i just beat that ass.
Norteno: Nah homey, you just ran up on that scrapa and hit him in the lip and let his true color drip. Puro noooorte.
Jefe: Puro todos shuten uppen.. Puro Beaten Assen!!!!!