Let me guess. OP's friend was the over-friendly farang who first came to Thailand thinking Thai people are smiles and sunshine only to realize its not that at all.
The friend made the mistake of giving a wai to a younger Beauty Pageant contestant who is from a society of classism, ego and face. To her being a pageant contestant, she has another added ego of layer on top of people watching her., so yes, she will not return it since she fears she will lose out on her class level.
This is the friends fault. And actually the contestant was nice enough to give a wai to the wife in public.
OP, your friend has to know the reality of Thailand, and once then, will he be able to enjoy its fruits.
Its the 'farang' cycle.
1)When they first come to LOS they tell the world how friendly Thai people. They see the smiles. They never been wai'ed before. They dont see the usual 'Karens' of Western Society.
2)After several years of living, they start to see the darkside that not all smiles are genuine and Thai's communicate 'indirectly' rather than directly. They become bitter.
As another posted pointed out, dont be the overly friendly guy that Thais can do know wrong, but dont be so bitter to the point where they think most Thais are like that.
I personally dont wai except to the much older in laws. Depending on the situation I may wai back (a great waiter who Ive seen several times at a local restaurant will I wai back as an example).