In my experience it goes one of these ways..
'Oh you are Buddhist, how interesting!' followed by nervous foot shuffling and a sudden need to refresh their drink.
'Oh you are Buddhist, how interesting !' followed by sniggers and jokes about my robes being in the wash.
'Oh you are Buddhist , how interesting!' followed by expressions of horror that I am in a pub/club/ party at all and noticeable attempts to avoid bad behaviour (as if their mother had just walked in the room).
Occasionally and refreshingly sometimes it goes ..'Oh you are Buddhist , how interesting!' followed by a respectful exchange of questions and answers, and a geniune curiosity to find out more.
I find that the reaction from people who knew me before I became Buddhist falls into two distinct camps. The first is an almost irritated discomfort that I am going through a 'phase' and a complete reluctance to discuss it with me, presumably waiting for me to 'get over it'.
The other is to notice the subtle changes in my behaviour and demeanour and become interested in finding out more if Buddhism has anything to offer them.
'Love removes the masks that we fear we cannot live without, and know that we cannot live within'