(this will include some Japanese, as anime has a huge slash fandom)

Flame - a nasty reply that has no purpose other than to insult someone.

Kai - Kyan/Jai relationship.

Kyson - Kyan/Carson relationship.

Lemon - term used to denote a sex scene in a story.

Make Better (MB) - the straight guy.

Shounen ai - (show-nen-eye) literally "boy love"; mild male/male love (i.e. handholding, romantic scenes, etc).

Slash - homosexual love and/or lovemaking.

Slasher - one who is a fan of slash.

Thai - Thom/Jai relationship.

Tharson - Thom/Carson relationship.

Yaoi - (yowie) Japanese acronym ("yaminashi ochinashi iminashi") that stands for graphic male/male love.