Thai food is not one cuisine — central, northern, northeastern and southern styles are dramatically different.
The baseline most visitors know — jasmine rice, clear curries, stir-fries, balanced sweet-sour-salty-spicy; milder than the other regions.
Sticky rice eaten by hand, khao soi (curry noodles), sai ua (herbal sausage), nam prik ong (pork and tomato dip) — more Burmese and Yunnan Chinese influence.
Sticky rice, larb, som tum, gai yang, pla ra (fermented fish) — the most popular cuisine nationally but also the spiciest and most pungent.
The fiercest cuisine — curries use fresh turmeric and dried spices; gaeng tai pla (fish stomach curry) is funky and extreme; massaman curry is a mild outlier.
Bangkok hosts genuine outposts of every region — Isaan restaurants cluster in working-class neighbourhoods, northern Thai khao soi appears at dedicated specialists, and southern curry houses are easiest to find near the Old City and Chinatown edges.
Central is the most forgiving for spice-sensitive eaters, followed by northern; Isaan and especially southern dishes assume a much higher tolerance, so ask before ordering if unsure.