[ctdonath]

Remember that both of you are running this app to meet using it, so you're already on the same page with "found with your phone". That's less creepy than tapping the shoulder of the guy in the next restaurant booth and asking "hey, are you interested in obscure topics X, Y or Z? ...sorry, just asking..." Even an amicable "just struck up a conversation" may very well not touch on topics which are rarely shared but are of great interest if known ("you took a course from Jeff Cooper too? [hours of intense chatting ensues]").