The Rice University Neologisms Database

Blatantly homosexual; one who is aggressive without provocation. Flamer, adopted by the homosexual community to refer to one of their own displaying stereotypical mannerisms, existed in the language for a long time preceding the use, usually referring to females (noted since 1781). Why it shifted is uncertain; it may have first been one of many words adopted as code by the gay community (gay, itself, another example of such a word). In this case, it was probably adapted metaphorically to refer to the glaring obviousness of fire—it may also be linked to the “passion” fire had previously been used to represent. Flamer moved into its second usage independently of the first, a back-formation from the verb “to flame,” likely derived as a synonym of “to burn,” used metaphorically to indicate a scathing response through the internet, yielding psychological symptoms similar to the painful injury it brings to mind.