1. He flirts with you, but doesn't ask you out
Ok, flirting can only go so far- to build suspense. If he flirts with you and doesn't care to actually take you out on a date and give you his time to get to know you- bad sign.
2. He sleeps with you, but doesn't want to be with you
If all he wants to do is sleep with you, but keeps telling you that he isn't "ready" for a relationship, then most likely he is getting what he wants and doesn't want you for anything more than that.
3. He spends time with you, when it's convenient for him
He can only spend time with you on Wednesday evening, because he is "busy" on the other evenings, and the weekends are off limits.
4. He doesn't believe in "labels"
He doesn't believe in using terms like boyfriend and girlfriend because he is above that, and no one needs to know his private life.
5. He leaves after sex
If he doesn't try to kiss you, cuddle or even sit down for a cute movie/snack then he is definitely not seeing you as more than a fun way to pass time and have sex