How do I ensure that he will not accept due to politeness?

Okay… so I’m about to ask a guy out…

I don’t want to waste my time on someone who will accept, and not reject, due to being polite, or not wanting to hurt my feelings. How might I make this clear as well?

I might also add that this is my first time asking someone out, or even telling them blatantly that I like them.

This guy is more of an acquaintance. I’m going to tell him that I like him, and then ask to go out. What shall I say after? Help me with wording..

And, what should I say if he rejects me? Any personal stories are very welcome.