Oca ti jebem
Commonly used in Montenegro... Means "I fuck your father"... It's an insult like "Fuck you" or it can be used like a threat...
Pusi kurac, oca ti jebem > Suck my dick, I fuck your father (here it is used as a threat)
Oca ti jebem ludog! > I fuck your crazy father (insult)
Oca ti jebem ludog! > I fuck your crazy father (insult)