Moister than an oyster
Moister than an oyster as a fun, rhyming wordplay is often used in reference to a woman’s genitals getting wet due to being aroused.
Comparing oysters, a rather attractive looking sea creature, to a vagina makes the phrase vulgar and humorous rather than sexual, and is meant to somehow eradicate arousal when talking about a sexual topic.
It is also a fun way to make someone uncomfortable.
The expression was soon added to images to create vulgar internet memes. The images used will often include unattractive or old people, just to add to the untasteful pun.
Oysters have historically been compared to the female genital, due to their moist, soft texture, and sometime even their looks.
They are also assumed to act as a natural aphrodisiac, hence, considering these historical sexual connotations to oysters, there is no surprise that such a slang phrase would arise.
The phrase appeared in February 2014, and had a massive peak in popularity around 2016.
Spread and Usage
According to Google Trends, Australia is a big fan of the expression, likely because Australians are major consumers of oysters in general, and the majority of Australians live next to the seaside, being prone to marine puns.
Following comes the US, then Canadians as a strong third.
Because of the general catchiness of the phrase, it has been printed on heaps of merchandize, and it’s easy to get hold of a cool t-shirt with the expression printed on it.
The slang has reached the music industry as well, inspiring the semi-professional song “Moister Than An Oyster” released in 2017, by Justin Abisror.