In my opinion the term "kill'em with kindness" applies well here.
My experience is that when i come across JWs which i used to know or belonged to my ex-hall, i make sure that i have a big smile on my face and am as nice and courteous as possible. There is something to be said about this...
I truly think that when an active witness sees an ex-JW which has a great attitude and seems happy, they are intrigued. They don't expect this. They are conditioned to think people outside of the Watchtower world, fall apart, are sad and unhappy.
I believe this is somewhat organic in human nature. Even in relationships there is a parallel. I recall breaking up with girlfrends and seeing them afterwards angry, bitter, avoiding me. This made me feel like i was better off without them.
On the other hand i recall a few which were completely fine with the breakup, and ready to move on. They continued to be nice, smile and being friendly. This intrigued me and actually made me feel that perhaps i really should be with them afterall.