slut line 

The horizontal line at the top part of tights, where there begins a boxer-shaped darker colored section. When this line becomes visible, you know that your shorts / skirt / clothes are probably too short and not very appropriate; you've crossed the slut line.

The jeans hotpants I wear today are so short, can totally see my slut line.

slut line by strawberrycrisp June 8, 2011

I'm not a slut line 

Where a woman, presumably a slut, makes an assertion, either verbally or by actions, towards her lack of promiscuity during the course of a sexual act with a complete stranger.

Dude, she was sucking on his dick five minutes after meeting him and was then uncomfortable with removing her bra as he was moving too fast, thats a I'm not a slut line if i ever heard one.

I'm not a slut line by Slaalaikum August 20, 2009

slutline tattoo 

a tattoo right above a girls ass crack

"Look at that girls slutline tattoo!!"

slutline tattoo by mrawesomeness August 22, 2008