That is, take an existing work of fiction and add or imply a homosexual subtext to it. Some do it because they find it amusing. Others do it because they find it arousing.
Most common targets for slashing are the Harry Potter and Lord Of The Rings books and movies. Macho movies, especially 'Top Gun' and 'Fight Club' are also favoured targets of this activity.
#2: For the love of all that is holy will you STOP slashing Shindler's List!