Just “คนไทยเป็นมิตร” Khon Thai pen mit mai? Sure most of Thai people are friendly.

คนไทยเป็นมิตร is Thai people are friendly. มิตรจิต also has the same meaning but it's a word we're seldom use for speaking. มิตรจิตมิตรใจ has the same meaning either. You may find this word in writting.

คนไทยเป็นมิตร means Thai people are friendly. Other words you can use are คนไทยอัธยาศัยดี คนไทยใจดี They have slightly different meanings, but the ones I suggested are a bit more informal and popular :)

Hi! Also interested in the answer. I used to use 'ben mit' but it never seemed to go down well!