Several sources, such as travel blogs, news articles, and forums (e.g., Skeptics Stack Exchange, Quora, Thaiger, and others), mention this no underwear rule. They often cite historical decrees or cultural norms rather than a specific, current law. Here’s what the sources suggest:
Historical Context:
Some sources point to a decree from January 15, 1941, during the era of Field Marshal Plaek Phibunsongkhram, which mandated that "Thais should not appear in public, populous places, or municipal areas without proper clothing." This included prohibitions on appearing in public wearing only underwear or no shirt. However, this decree and other similar cultural mandates were reportedly repealed by 1944, according to historical accounts like "Fall of the Phibun Government, 1944" (page 117).
Current Legal Framework:
The Thai Penal Code, particularly Section 388, addresses "indecent acts" in public, which includes "shamelessly exposing oneself or committing other indecent acts." The penalty for violating this section is a fine of up to 500 Baht. While this section could theoretically be interpreted to include not wearing underwear if it results in indecent exposure, there are no documented cases of people being prosecuted specifically for not wearing underwear under their outer clothing. The law focuses more on overt public nudity or behavior that offends public morality.