You're all about knocking heads and beating Skulls.
How to Get
Defeat 50 Bone Daddies.
Hero side, the easiest way to get this badge is to hunt Bone Daddies in the Boneyard area of Perez Park, the Northwestern most section of the map. It is advisable to do this at a higher level, where it's possible to just run from group to group of Skulls, killing Bone Daddies and ignoring the others.
CoV: If you have missed the Skulls in the early newspaper missions around Lv. 14 you can use the Flashback-System: There are three Bone Daddies in the second mission of Dmitri Krylov's story arc "The Vahzilok Conference".