I'll start with the bad news: Kao Niaw Ping Kai Restaurant is located on one of the least inviting stretches of Budapest, the multi-lane Rákóczi Road, where the constant stream and pollution of car traffic has all but cleared the area of pedestrians. But don't despair. A quick bus-ride from downtown (take #5, #7, #110, #112, or #178) will drop you right outside the restaurant, so you won't need to inhale any exhaust fumes.
Inside is one of the best casual Thai restaurants of Budapest. Although Kao Niaw Ping Kai advertises itself as a Thai-Laotian fusion place (the owner-couple is a Thai-Laotian duo), the menu delivers the standard pan-Thai fare, featuring curries, and stir-fries, and coconut soups. There's also a section dedicated to spicy dishes from Isan, the northeastern region of Thailand bordering Laos. The interior furnishings are a step above standard takeout decor, meaning that a laid-back date night woldn't seem out of place here.
As for food, all dishes are solid. You can't go wrong with the pungent green or red curries (€7), and the familiar stir-fry dishes—pad see ew, pad thai, drunken noodles—also beat the local competition. I'm pretty sure that the nam tok moo (€8), a pork salad with green herbs, is one of the spiciest dishes in Budapest. All the more reason to leave room for the coconut-tapioca pudding that will soothe your burning mouth (€3).