You've seen it a 1000 times before - someone walking, perhaps riding a bike or scooter with their full attention on their phone in their hand, completely oblivious to the world around them.
They're either self-centred, addicted to their phone (due to an overwhelmingly desperately empty life outside of it), or engaged in a must-read message/game of Angry Birds at that point.
You've seen them, because your head is NOT up your ass, and you do assess your surroundings periodically, especially in a very full place like Taiwan or China.
They're on a crash course collision with you.
A - step aside to let them walk/ride/drive past, nose to the phone
B - yell out a "whoop whoop" to pull them out of their world, and let them know you're coming the other way
C - hold your line, and let them crash into you (human on human, I'm 87kg, works a treat if/when I do it)
My friend reckons that they're working on the theory of 'if I haven't seen it, I don't need to acknowledge it, therefor it doesn't exist', and we as the see-ers 'have seen and acknowledged, thus must move'.