Shit mother dick is a phrase that is often used by 5th graders who think they know how to swear.
Example:
Teenager: Crap, I dropped my backpack
Kid: We're allowed to swear here?
Teenager: No you can't swear here you're like 8
Kid: Shut the fuck up I'm 11 you little shit mother dick
a combination of holy shit and mother fucker: an exclamation of excitement and/or approval
Shit Mother! The Steelers kicked some ass yesterday! You know it.