Dude is a bit like the word mate, isn't it? I'm not just from London. I've also lived in Liverpool and Birmingham so some of my slang might be a little bit regional. Faff means to mess around or procrastinate - but sometimes that can mean negative things too. A fancy would be when you think someone is really good looking and you find them sexually appealing. John fancies her because she's really hot; he likes people who are 'really fit'