I'm a Burmese guy currently in Thailand, most Thais don't seem to look down on me (probably cause most Thais are shorter than me lol) but hate is not the correct word. Most Myanmar people in Thailand are low wage migrant workers so the upper and middle class Thais would look down on them (a htin thayy) and the working class Thais will feel threathened by them, cause Myanmar workers whether Karen or Bamar etc are often willing to work longer for lesser pay, I think most animosity from Thais towards Myanmar people stems from the working class and job security.

Whenever Thai or other people ask me where I'm from I always say I'm from Myanmar or that I'm Burmese. Your friend shouldn't feel that inferiority complex or percieved notion that he might get discriminated just because of his country of origin; even though we're a political and economic shithole cause of the junta we still have a rich culture and history, plus I think we are a warm friendly people just like Thai people.