smash (one's) head in
To strike one in the head or the head with intense, violent force. The cops arrested the man after he threatened to smash their heads in. Where's the guy who insulted you? I'm gonna go smash his head in!
smash somebody’s ˈface/ˈhead in
(British English, informal) hit somebody very hard in the face/head: Give me the money or I’ll smash your head in.