The informant states that the above Thai curse word is also the name of an animala lizard that looks like a baby crocodile (the animal is called a water monitor in English). Thai people claim the reason why the curse word and the name of the animal are the same is because in the past a lot of farmers raised chickens, and this animal would come out of the canal and eat the chickens, and it was believed that if you saw this animal that it was bad luck. The informant learned this item from friends at school when he was around 12 years old. He states that he would tell the story only to his friends, and not to anybody older than he. He believes that the story is correct and that this is the reason why the word is used.
The story that the informant tells of why the Thai equivalent of our curse word fuck is also the name of a certain reptile found in Thailand is an instance of meta-folklore with a sort of very brief legend being used to explain the etymology (thus, folk etymology as well) of this piece of Thai folk speech. It seems quite possible that if the story in any way represents the actual cause of the conflation of the two meanings of the word, then the English translation as fuck might not encompass all the same possible connotations. Instead the Thai here, would seem to express, or in some way relate to, a cause of misfortune (since it refers to a creature who, according to the story, represented bad luck, particularly in that he would eat the farmers chickens) whereas the English fuck would not, instead being mostly used as a form of (vulgar) reaction to an disagreeable circumstance.