LSS can also be known as LS Syndrom. LSS stands for Love Struck Syndrome and it's when you love/lust for a guy or girl physically and/or mentally, whether you've dated them or not.
You see your bestie drawing hearts all over a piece of paper, looking distant with a odd look in their eyes
You say: Dude, do you have LSS because it seriously looks like it.
Then your bestie blushes really hard and looks away.