How can I get my new kitten used to wearing a collar?
He tries to take it off and I feel so bad and end up taking it off. But I want him to wear a collar! How can I get him used to it without it bothering him so much?
You need to be persistent and consistent. Keep the collar on but like what everyone said, make sure it's not too tight. Breakaway collar is the best option. Make sure you do not remove the collar whenever he whines. He will try to take it off because it doesn't feel right for him. I don't put a collar on my indoor cats because they don't need one, I microchipped them for ID.
Some cats though will never get use to it. So, if there is no good reason, just let him be. 
