While Chinese as a language has plenty of scope for pouring scorn on people verbally, visually it is a different story.
Now, China also is no stranger to hand gestures as this Sinosplice article about counting on one hand relates (personally, I've always assumed that this developed not to vercome the language barrier with so many regional dialects but simply because bars and restaurants are so noisy with everyone shouting all the time that people can't hear each other across the table when they're playing the dice game).
Chinese body language can be incredibly unintelligible. One of my early trips to Hangzhou took me to a shop with an interpreter who spent twenty minutes with the shopkeeper yelling at her with his face an inch from hers (close enough for her to need a tissue when the conversation was over...) and it was only when they reached a conclusion and I heard him yell "谢谢.没问题!" (Thank you. No problem") at her did I realise that it was simply his manner, rather than him actually being livid.
So, with a litany of swear words, a familiarity with hang gestures and hard to read body language, why is it that no common Chinese hand gesture exists that conveys the notion that you are somehow displeased with another person or as pete has suggested, that you have no way of conveying to another driver the sense of "I, personally, disapprove of your most recent manouevre".
I lost control briefly whilst driving to work this morning and found the (two-way) road completely blocked with cars coming towards me and my attempt to convey displeasure at the driver coming directly at me left him with a puzzled look on his face which I interpreted as "Two? Why is he saying two?" (hint - I'm British - if I was American he'd undoubtedly have assumed I was saying one). Definitely time for a Chinese standard gesture...