When you don’t like your date, you don’t just not like your date… but you see every little flaw and every little tick and every little everything that bothers you.
It’s called the Ick Factor. Once someone bugs you, then you see all the things about them that wouldn’t have normally bothered you. When you don’t like someone, then you will either look for things wrong with them or things will just pop out and annoy you to no end. When you know someone is wrong for you, then you will notice and get icked out by the way they talk, laugh, chew, walk, sit, stand, and basically, exist. Those things wouldn’t bother you if you liked the person.
Realize that this is normal, this is not a match, maintain your dignity, and — after the date — thank the other person for a nice time and move on. Don’t try to see if the ick factor will go away — it won’t.