1. The girl who’s super insecure

Confidence is sexy. And insecurity is, well, a good sign that you might want to wait before sleeping with her, says sex therapist Kat Van Kirk, author of The Married Sex Solution: A Realistic Guide to Saving Your Sex Life. “Women with poor self-esteem could often look for validation through sex,” Van Kirk explains. “She could get attached very quickly.”

That doesn’t mean she’s a bad person or that the relationship is doomed. It just means casual sex may not stay casual for long. When someone is constantly putting themselves down—especially about their appearance—they may be looking for reassurance rather than a fling. If she’s always criticising her looks or fishing for compliments, it’s a sign she may be tying her self-worth to your reaction. In that situation, sleeping together can blur emotional lines quickly. A woman who’s always denigrating herself—particularly her looks—isn’t the best candidate for a no-strings-attached arrangement.

2. The Gold Digger

You don’t need to be wealthy to attract someone who sees relationships as transactional. If she shows a strong sense of entitlement—for example, never offering to pay for a date or talking about past relationships in terms of what she received rather than how she felt—sex might come with expectations attached. “You want to understand her value system,” Van Kirk says. “Does she see sex as something mutually enjoyable, or as a way to get what she wants?”

Pay attention to the small signals. If every night out seems to revolve around what you’re spending, where you’re taking her, or what she expects next, that’s a clue about how she views the relationship. Casual sex works best when both people see it as a shared experience, not a negotiation. When someone treats dating like a series of transactions, intimacy can quickly turn into leverage—and that’s rarely a good foundation for anything, casual or otherwise.

3. The Party Animal

There’s nothing wrong with enjoying a night out. But if you’ve never seen her sober, it might be worth pausing. “If she can’t have fun without getting drunk, that may mean she’s uncomfortable in the situation,” Van Kirk explains. “It can also signal poor judgment.” There’s also the obvious issue of consent. If someone is intoxicated, they can’t properly consent to sex.

It’s also worth paying attention to patterns. Everyone cuts loose now and then, but if every date ends with shots, sloppy behaviour, or memory gaps the next morning, that’s not just a party habit, it’s a warning light on the dashboard. Alcohol lowers inhibitions and clouds judgment, which means decisions made in the moment often look very different the next day. That’s how casual situations suddenly become messy ones.

If you’re looking for something uncomplicated, it’s better to see how someone behaves when they’re clear-headed. Confidence, humour, and chemistry should still be there without a couple of drinks doing the heavy lifting. And frankly, if the connection only exists after three cocktails, that connection probably isn’t real in the first place.

4. The Girl Who is Casual About STDs

Her sexual history isn’t the issue—everyone has a past. What matters is whether she takes sexual health seriously in the present. If you’re getting close and the subject of protection or testing never even comes up, that’s a flashing warning sign. “Both partners need to be responsible for their safety,” Van Kirk stresses. If she’s not even slightly concerned about her own well-being, you can bet she’s not thinking about yours. Safe sex isn’t optional; it’s a basic respect.

5. The Woman Who is Never Single

Now, about the woman who’s never single. Sure, you might finally get your shot with the woman who always seems to have a boyfriend. But according to relationship expert Tracy Thomas, PhD, that pattern often hints at something deeper. “People who are always in relationships tend to lack a strong sense of self,” she explains. If she’s only ever defined herself as one half of a couple, she may struggle to navigate life solo. Once things turn physical, that dependence can escalate. In other words, what starts out fun could quickly turn into a clingy dynamic if she’s seeking her sense of self in the relationship.