A very bad smell. Stinky.
A combination of the words: 'skunk' and 'anus'.
Background information: My Scottish mother-in-law (I'm Canadian) and are always (jokingly) finding new ways to insult eachother. 'Skaynus' was a new way!
eunice: "danny was cracking jokes at the party last night and everyone was laughing so damn hard until Simon came in and instantly slayous'd the party..."