Shoneen is the diminutive of shone [Ir. Seón]. There are two Irish names for John--one is Shone, the other is Shawn [Ir. Seághan]. Shone is the "grandest" of the two, and is applied to the gentry. Hence Shoneen means "a little gentry John", and is applied to upstarts and "big" farmers, who ape the rank of gentleman.
Sleiveen, not to be found in the dictionaries, is a comical Irish word (at least in Connaught) for a rogue. It probably comes from sliabh, a mountain, meaning primarily a mountaineer, and in a secondary sense, on the principle that mountaineers are worse than anybody else, a rogue. I am indebted to Mr. Douglas Hyde for these details, as for many others.