How can I show him that is ok to be comfortabe around me ?

sorry if this is a lil long...ill try to keep it short :p 14 yrs. I like him, and heaps of people have to me he likes me. I dont want to date him at the moment (eventually, just not now though) but how to i get him to be more comfotable around me. When he first starts a conversation with me he's usually a bit distracted and sorta says insulting things (e.g sarah is a half binhalf mutant terrorist . If the conversation goes for a while he gradually starts to settle down. one day we spent the entire day together (in a group)by the end of the day he seemed really comfotable around me (at the end of the day We were sitting at a table and he came a sat next to me really close when there was heaps of room, i had my bag on the table and he started going through it and putting my sungles on) so my main question is how can i get him to be comfortable around me all the time instead of being closed up ? Any ideas other than "just tell him how you feel"? thanks! i really appreciate the answers!