You will be in BKK on the most important holiday in the Kingdom (IMHO) - His Majesty King Bhumibol Adulyadej's Birthday. I was lucky enough to be in BKK on this date - and stood on the street holding a candle with locals as HM the King rolled by in the yellow bentley (or was it a Rolls) .....

BTW - everything in the country will be CLOSED!

Info Here

An important public holiday is held on 5 December to celebrate the birthday of His Majesty King Bhumibol Adulyadej, the world's longest reigning monarch. Known in Thai as 'Wan Chalerm', the occasion is marked by an outpouring of love and reverence by Thai people throughout the kingdom and around the world.

On 5 December, buildings and homes all over the country are elaborately adorned with flags, portraits of His Majesty and bunting, predominantly in the color yellow. Around the Grand Palace and Ratchadamnoen Avenue areas of Bangkok, thousands of vividly colored marigolds decorate the streets. On the evening of the holiday itself, the streets around Ratchadamnoen and Sanam Luang are closed to traffic and thousands of people take to the streets. Spectacular fireworks displays are held and the atmosphere is joyous and festive. The best way to enjoy the atmosphere is to take a bus to the Rattanakosin area, and just stroll along the crowded but traffic-free streets for a truly memorable experience.