Yikes I've never had a stranger try to strike up a conversation with me when I actually have my headphones in. Although I did have someone try to strike up a conversation when I was sat there read a book one time, like urgh fuck off. A brief comment on having read the same book/or asking if it's any good is all good, but if the person doesn't then pick up the conversation but immediately returns to her book, then hello take a hint and stop trying to engage her in conversation

I guess I've been pretty lucky though becase 9 times out of ten when someone sits next to me because the bus is full, it's generally acknowledged as a bit of an awkward thing and no conversations are ever started up. I find it's more of a problem if you're traveling long-distance, it always seems to be old men nattering on so I feel like I have to be polite and humour them, but generally on short journey's into town everyone seems to keep to themselves thankfully