O léxico do RPG.net define como:
Illegitimate enjoyment. Saying that a game is "bad wrong fun" indicates that the game is somehow broken, unplayable, poor quality or weak - in ignorance of the fact that many groups are playing and enjoying it regularly. As such, this is not normally something that a person will say themselves, but something they will accuse other people of having said. For example, "John said that d20 is bad wrong fun" indicates that the speaker believes John's criticism of d20 to be foolish given the large number of groups playing and enjoying it. Rifts is often cited as a "bad wrong fun" game. Often written as a single word, badwrongfun.
"Bad wrong fun" is also often used in a more light-hearted sense to indicate the gamer equivalent of a guilty pleasure. "I know it's bad wrong fun, but I loved every minute of it!"
A referência mais antiga que eu posso encontrar para o seu uso é de
A questão me interessa, pois é claramente um conceito que não é peculiar aos RPGs. Por exemplo, partidas de futebol podem ser ruins para pessoas que preferem ópera. Como tal, eu publiquei isto pergunta em nosso site irmão English Language & Uso para descobrir que outros termos existem para o fenômeno.