CULT BUY: The $18 liquid eyeliner so unsmudgeable, it's "sex-proof".

What do you look for in a liquid eyeliner?

Super black? Affordable? Foolproof to use?

… How about sex-proof?

If that’s the case, step right this way because BOY do I have an unsmudgeable recommendation for you.

Beauty lovers are raving about the NYX Makeup Professional Epic Ink Liner for exactly that, according to Allure.

Reddit user okra_ shared her review on the makeupaddiction subreddit earlier this week, claiming "everyone who wears liquid liner NEEDS to invest in it immediately".

"I have been using it now for the last month or so and it is absolutely AMAZING and stays put through everything," she wrote.

"I know you're not supposed to keep your makeup on overnight (and I'm normally good about it) but I've fallen asleep multiple times drunkenly at a friend's place or had unexpected adult sleepovers (lol) and when I wake up the next day everyone (including me) is absolutely amazed at the fact that it still looks PERFECT every. single. time!!!"

She's also developed a trick to ensure it really doesn't budge.

"I pair it with the NYX matte setting spray for double protection," she says.

And if you're looking for a slightly less NSFW quality, another user said it was tried and tested for being waterproof.

"I wore it in the shower once, and it didn't budge even slightly," they added.

While NYX products are widely available in places like Priceline and Target, it doesn't look like this particular liner is available there yet. The good news? You can order it from ASOS for $18.

With a fine-tipped brush, it's perfect for creating thin or thick flicks and the fact that it's waterproof makes it great for oily skin/eyelids too.

At least it's one thing you can rely on to last a long time in the bedroom.

For more beauty and style stories, you can follow Brittany Stewart on Facebook and Instagram.