1) A ridiculously incompetent or underperforming individual in a particular area,
2) An extremely prevalent disappointment,
3) A person whose vocabulary routinely involves profanity and biological accusation and is generally a cock,
4) Something with low-standards.
2) Mate! You see that fookin' goal last night? What a fookin' gaviscon mate!
3) "You all fondle children and **** yourselves in the ****ing ******* you ****ing ******"
"Sod off, you gaviscon."
4) Hello, I'm Jeremy Clarkson, and you're watching Top Gear.