A commonly used abbreviation from the song lyric in "Brain Damage" from Pink Floyd's album The Dark Side of the Moon that goes "I'll see you on the dark side of the moon". Another common variation is TDSOTM to stand for the album name.
And if your head explodes with dark forebodings too,
ISYOTDSOTM.
Iyktv is an acronym for If You Know The Vibez. This is usually used as a way to explain potentially sexual conversation topics without giving a definite answer or as a way to make light conversation with tight friends.
Frank: Hey how’s it going withSamantha man 😉?
John: Oh it’s going well 😈, iyktv🥴.
Frank: Niceee 🤝
guy- well, see ya.
girl- ilykthnxbai
guy- what the heck does that mean?
girl- oooh nothin.
*Girl is obviously shy around this sexy boy, so she's used netspeak to cover up her words.