First dates are filled with uncertainty. You may find someone you really connect with, or at the very least, you might learn something new about yourself. But, not all first dates can be something out of a movie. Some, unfortunately, come with red flags, dealbreakers, and disappointment.
Maybe your biggest pet peeve is tardiness, and there's nothing you hate more than someone who doesn't respect your time. If your date is more than 15 minutes late without warning, you know the connection is doomed. Even if they seem alright in person, you hate feeling like your time isn't valued.
Perhaps talking about an ex on a first date is a dealbreaker for you. If your date happens to casually mention an ex in the context of a larger story, that's fine. But, if they go into detail about their ex, say why they broke up, or list negative qualities about their ex, it's over. Though it's totally reasonable for people to have toxic exes, you don't like unloading that kind of baggage on a first date. Plus, if someone starts going off right away about how their ex was the problem, you know THEY are probably the real issue.
Or, maybe you can't stand when a date orders for you, especially on a first date. When you don't really know someone and haven't had time to learn about their tastes, you think ordering for someone is tacky. You're fine with hearing their recommendations, but if your date orders your food or drinks, you're done with them.