Gammon is a pejorative popularised in British political culture since around 2012. The term refers in particular to the colour of a person's flushed face when expressing their strong opinions, as compared to the type of pork of the same name. It is characterised in this context by the Oxford English Dictionary as occurring "in various parasynthetic adjectives referring to particularly reddish or florid complexions".
In 2018, it became particularly known as a term to describe either those on the political right or those who supported Brexit. Due to its referencing of skin colour, there is controversy as to whether the term is racist.
I assume that the person that used that racist term over on the Darkside board has been banned from posting