While the word gaviscon is commonly attributed to a certain brand of heartburn and indigestion treatments, it has a completely different meaning that has not entered even the simplest of household vernaculars.

It means:
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.