Smegface is the Red Dwarf equivalent of Shitface, Fuckface, and other insults of that sort.
"Smeg" is a general-purpose swear word made up by Grant Naylor (the collective name of Doug Naylor and Rob Grant) for the Sci-fi Sitcom Red Dwarf, in order to get around language policies in TV.
The word was
inspired by an Italian home appliance
manufacturer going by the same name and not by smegma, like the first
impression might rightfully suggest.