Funny that he's from the UK and called you an American twat. I have had so many similar paypal disputes from people from the UK, who never feel the need to email me with their problem first, before starting a dispute that I eventually win.
Obviously everyone from the UK isn't like this, but there have been numerous times when someone files a claim on me and then will argue calling me a fat american, etc. I don't know what it is with people from the UK or their problem with Americans. I don't know if they are just more angry/aggressive or if they are just more high strung. I have always been polite and there have been 3 instances where UK buyers would completely freak out via email or in paypal disputes and always feel the need to point out that I'm an American or tell me to go eat at McDonalds.
Again, I'm not saying all people from the UK are like this, it's just been my experience thus far with people disputing service/items on paypal. Politeness goes a long way with me, when someone argues with me, I'm a lot less likely to help the person out. Just my personal experience!