Patpong Night Market
Here you will find knock off everything from Tiffany, Rolex, Louis Vuitton, to course loads of Diesel. If you are interested in buying fakes, do buy in moderation, as the Lanham Act (US) steeply penalizes possession or distribution of knock-offs. I have not heard of a tourist being busted with a fine or jail time, but I have heard that the items will be confiscated. The prices at the market are cheap, but you do have to deal with the locals who are peddling goods and just may push you to the edge.
The faint of temperament should not visit this night market as you will find it quite vulgar. Men will try to sell you tickets to X-rated shows and ask you to try on various clothes or buy DVDs. It doesn't seem to matter if you are there with a guy, they continuously flock you for business. No matter how many times you tell them you are not interested, they follow you for blocks... not to mention the go-go dancers that beg you to come to their shows.