Although I've learned to be more careful about who I talk to my friendliness has never really waned. I think it is partly due to the fact that I've lived in pretty sheltered environments my whole life. In my neighborhoods and schools in Maryland and Minnesota, at Denison and even in Vienna and Zürich people always greet one another. Even if you don't know them you'd smile and say "Hey," "Hello," "Hi," "Grüss Got" or "Grüezi." I feel very lucky to have lived in safe and friendly locations but sometimes, especially living in a country where you don't speak the language, it can be tricky.
I guess something about me says, "Hello strangers! Please talk to me!" If some wacky weather or slightly humorous situation is occurring whoever is by me on public transport will make a comment. This is usually no problem and I can smile, nod and either laugh or say "Ja, ja." Language barrier avoided and they think I laughed at their joke, everyone is happy!
Although I don't think I'll ever be un-friendly, I mean I've made some amazing friends because I've sat next to them and started talking but, I'm not exactly sure how well this will work in Istanbul, but I realize I'm going to have to be a lot more careful. Maybe I should re-read that Berenstain Bears book.