Now and till 2nd of October there is a vegetarian festival in Bangkok which is called (เทศกาลกินเจ Tesagan Gin Jay)
First I want to describe the common situation about vegetarian food here.
Normally for centuries Thai people cook on pig fat, and make soup from pig bones. So if they fry vegetables they do it on the pig fat, and if they cook rice noodles from pig bones.
Also Thai people do not consider fish, chicken and pork like an animal meet at all. Animals are ox, goat, sheep, horse etc. but not pig and chicken.
So when you will ask a person to serve food for you without meat Thai people very likely will make for you: vegetables fried on pork fat with chicken, pork soup noodles with chicken meat or pork balls, salad with tuna.
So in this mess you will ask me where is real vegetarian paradise?
Here is it 23 September – 2 October and if it is not enough 24th October – 1st November second time
Nowhere in Bangkok celebrates the Thai Vegetarian Festival quite like China Town does. Chinatown (ถนนเยาวราช Yaowarat Road) is naturally where the center of all the action, particularly in the evenings.
You can get easily from my place by MRT.
The best way to enjoy all the delicious vegan cuisine is to just walk through the area surrounding Yaowarat Road and sample small dishes at some of the hundreds of temporary stalls.

If you feel like everything nice and wonderful about vegetarian festival well I can tell you it is definitely not, but not in Bangkok this time in Phuket
Devotees participating as mediums (Rang Song ร่างทรง /râang song/ or Mah Song ม้าทรง /máa song/) bring the nine Taoist emperor gods to earth by entering into a trance state and piercing their cheeks with all manner of objects: sharpened tree branches, spears, slide trombones, daggers. Some even hack their tongues continuously with a saw or axe blade.
Those chosen for possession may be men or women, young or old. There are many reasons for a god to choose a particular person. It could be that the person is about to die for some reason and becoming a mah song is a way to extend their life. Or it could be that they have bad karma from an earlier life, and something bad is about to happen that can be averted if they become a mah song. Some people believe that, in some cases, the mah song has some deep historical connection with the god. But whatever the reason, no one can become a mah song without the permission of his or her parents being sought.
They believe that the gods skewer the cheeks of the mah song with objects as a way to absorb bad energy, to help other people by freeing them from bad karma, illness or sorrow.
Shopkeepers on central streets set up altars in front of their stores, offering incense, fruit, candles, flowers and nine tiny cups of tea to the deities invoked throughout the festival. During the street processions, mediums stop at the altars and pick up the fruit, which they add to the objects piercing their cheeks or pass on to bystanders as a blessing. The mediums also drink one of the nine cups of tea and grab some flowers to stick in their waistbands. The shopkeepers and their families look on with their heads lowered and hands together in a prayer like wâi gesture, out of respect for the mediums and the deities possessing their pierced bodies.

Some people do it out of religiousness being very strict about all the rules of the festival, while others do it light-heartedly just for the taste and fun of it. Yet others do it for a change from the regular intake of meat in order to give their intestines a break, and to enjoy and not miss out on the palatable vegetarian available dishes only available during this time of the year.
If you are interested to participate in this festival, here are the 10 practices you should follow:

1. งดเว้นเนื้อสัตว์หรือทำอันตรายต่อสัตว์
Refrain from eating all kind of meat or do any harm to animals.
2. งด นม เนย หรือ น้ำมันที่มาจากสัตว์
Refrain from having milk products, butter or oil from animals.
3. งดอาหารรสจัด รสเผ็ดมาก เค็มมาก หวานมาก เปรี้ยวมาก
Refrain from strong flavored food, very spicy food, very salty food, very sweet food, very sour food.
4. งดผักกลิ่นฉุน 5 ชนิด คือ กระเทียม หลักเกียว หัวหอม หลักเกียว กุยช่าย ใบยาสูบ รวมทั้งเครื่องเทศที่มีกลิ่นฉุน
Refrain from five strong-smelling vegetables which are garlic, Elephant Garlic, onions, Garlic chives, tobacco leaves as well as strong spices.
5. รักษาศีล 5
Practice the Five Precepts or rules of morality
•to abstain from killing
•to abstain from stealing
•to abstain from sexual misconduct
•to abstain from false speech
•to abstain from intoxicants causing heedlessness
6. รักษาจิตใจให้บริสุทธิ์ purify the mind
7. ทำบุญ ทำทาน นุ่งขาว
Make merit, wear white clothes
8. ไม่ใช้จานชามปะปนกัน
Use kitchen utensils separately from others not used during the festival
9. งดดื่มสุราและของมึนเมา
Refrain from drinking alcohol
10. Women having their period should not attend any rituals.