A few visits ago at Sripraphai, I saw some Thais order a noodle dish I hadn't seen before.
The server told me it was a variation of N18, Noodles in soup with meat and vegetables. You ask for it dry, with seafood instead of meat, and chili sauce on the side to pour over the noodles.
When we tried this dish on our next visit, it was delicious. Glass noodles tossed with shrimp and squid, slightly bitter greens and a bit of egg. The sesame-chili sauce on the side was smoky and not so hot. Perfect for a cold evening.
Since I never would have known about this dish if I hadn't seen it, I am hoping other Chowhounds will share their off-menu favourites at Sripraphai.