i used to be incredibly shy, but over the years i've learned to be very friendly upon meeting others. so, at first i come off quite social and friendly, making it a point to introduce myself to others and make light jokes. people find me quite charming right off the bat.
however, the next time i meet you, i might be a bit more aloof. much more quiet. or keep it on the same friendly level as the first time.
but if it comes down to actually sitting down and chit chatting, i'm a bit more closed lip. i'll tense up in these situations if i'm not very familiar with you.
and for me, familiarity takes running into you about 50 times first, slowly getting to know you. haha.