Why do cats headbutt you?
Cat is very fun loving animal. They get familiar with people who cares for them easily. Headbutting shows that a cat is feeling familiar with you. By headbutting they are expressing a familiar relationship and using scent as a marker.
By doing this they are using some of their scent glands, (cheeks, lips, forehead) to leave their scent on you or another object.
Headbutting also help a cat to bond with other cats and it is their way of mapping their “safe zones”.