of course thais also smile in happy or friendly situations.
but there are only a few kinds of smiles for these situations.
one of them means I am so happy Iam crying
(yim thang nam taa)
Thais use it when they are very very happy.
Another one means " I respect you"
(yim cheun chom).
Finally these is the smile for people you don't know
(yim thak thaii)