Fob,
  Did your friend force you to put on "dosalla"? It's is gurungs gathering, what do you expect him to wear? Do you expect him to wear dhoti? How is he forcing his culture on to you? I am very curious. 

 I think we can still be Nepalese respecting difference between us. Let us celebrate diversity within us, rather than trying to homogenize entire population and alienating some.

 It is good thing your friend is promoting his own culture. Atleast he has not forgotten his roots. Why can't you accept his identity? Or is it because you have no culture. 

 "dosalla", "Haku patasi" are also part of nepalese culture It is very unfortunate your narrow mind didnot have capaicity to process this information, It is thoughts like yours which view entire Nepalese population consist of only certain cast of people which is helping fuel ethnic divide in Nepal. 
 
I can understand your feeling if your friend was chanting "Limbhuwan", "tamanagsaling" n stuff. But, just because he put on "Dosalla" in gurung gathering you felt so...shame on you. 

 Go through first line of new Nepalese national anthem.. Maybe you will learn something.