Definition: a contemptible unmannerly person
English is a language that contains an embarrassment of riches for when one wants to say something mean about someone else. If you need to refer to a contemptible person you may choose from blighter, cockloche, dandiprat, dirtbag, dogbolt, shagrag, stinkard ... you get the picture. So why do we need smatchet? Well, because there are a lot of contemptible people out there.
And you, ye idle ablich ‘at ye are! negleckin yer business an’ galantine aboot wi’ yon blackguard smatchet o’ a loon, Geordie Onnerson.
—James Leslie, The Otter’s Tale-Book for the Winter Evenings, 1839