Not sure about Beijing but when I was in Shanghai our hired
passenger van driver did the same thing. However I notice that no
one uses middle finger or gets upset they just honk and everyone's
used to it. If you use your horn in Singapore, drivers tend to get
upset very easily. I think it's mentality in the end. I noticed
that many drivers here assume once they signal, it means you must
give way to them. Some straddle both lanes to see which one will be
faster, some signal once then zip into your lane, some come into
your lane first then signal.
In Singapore, often if there are multiple lanes at a red light and
all lanes except one, (let's assume lane 1) are already occupied, a
person who's approaching from behind in lane 3, 4 or sometimes even
5, will cut across the whole carriageway so he can be the first one
in lane 1 at the light. I generally assume he's going to be going
faster so I'll stop behind him at lane 1 too. 7 out of 10 times
that person will be the slowest of the 3 lanes even though lane 1
is supposed to be the fastest, overtaking lane, whether it's on a
normal road or expressway. Don't believe me try it yourself.