Is it normal to not know if you like someone?

If you don't know, give them a neutral answer.

I think it's normal - sometimes certain people just don't inspire a strong reaction - you can't like everybody. How well do you know them?

when you didn't expect that one friend to like and your just uhhh... how do i say no thank you without being mean

Attraction is a weird thing. I definitely don't think it's as simple as "you know it when you feel it". It comes in degrees, and there definitely is a grey area. There are lots of people who have some traits I find sexually and/or romantically attractive, but have other traits I don't find attractive or find actively unattractive. That state definitely exists.

If you were asked out by someone you felt that way about, I would go for it. The worst that can happen is you get a bit of dating experience with a person you find at least moderately attractive. Nothing bad can come from giving it a try.

you can toy with the idea, maybe spark your own interest but if you decide against it, it's likely to hurt them.

Tell them that your friend is in the "Friend Zone".

Do you mean "like" as in the feelings you would have for a friend, or as in a sexual relationship?

Either way, when you know a person quite well and you don't enjoy being around them enough to want to be around them some more, then don't bother.