Brownhatters (also known as: Uphill Gardeners)
Brownhatters is Jackspeak for homosexuals/gays.
Until January 2000, homosexuals were officially banned from serving in the UK's armed forces, a change only coming about following the defeat of the British government in the European Court of Human Rights, following a long campaign to lift the bar on serving gays. Despite the official ban, homosexuals served in all three services, their reserves and auxiliaries. In the RN homosexuals were sometimes tacitly accepted by individual commanders or members of a ships company, especially where the person was popular with their shipmates.
There is still residual hostility to homosexuals within the forces, as in society at large, but in the RN this is no longer officially tolerated.
Banter often centres around perceptions of stereotypical behaviour, so that in the case of gays, there will be banter about watching your back, the need for soap-on-a-rope and avoiding bending over in the showers. Likewise, references to the Golden Rivet, which newbies are often baffled by, hint at male-to-male buggery, back in the days when ships were all male.
See also: Rugmunchers, Golden Rivet