Phrases

Does anyone know what these phrases / sentences mean ? I found them in a novel set in Northern Ireland.
"Don't be such a slitherum dick"
"you're a big man but a wee coat fits you"
"there is nothing to it since Vatican Two"
"boys shouldn't squander their meagre resources by hazarding them on the comparative velocities of canine or equine quadrupeds" (supposed to be a joke)
"the boys sang Republican songs"
Cheers
Allie