Now that's a spicy a meatball! (ISO spicy food)
It's been awhile since I've been, but Orochon ramen near downtown used to offer grades of hotness in the ramen, and if you could eat an entire bowl of the highest grade, you get your picture on the wall. Not may favorite ramen place in L.A., but extra points for crazy spicy-for-spicy's-sake.
I second the papaya salad at Wat Thai. But also the papaya salad or the Jungle Curry at the Thai restaurant Yai in Thaitown. That Jungle Curry kills me everytime.
For non-Thai, try any of the "water boiled" (a misnomer if there ever was one) dishes at the new location of Chung King on San Gabriel and Mission. They may call them _ in spicy sauce or broth or something - I forget exactly.
The spiciest dish in L.A. is reputed to be the Shrimp Topolobampo at Babita Mexicuisine in San Gabriel. I tried it about a month ago. The shrimp is cooked in a very, very, very spicy--but also very tasty, fruit--habanero pepper sauce. I'd order it again, but probably not right away.
Definetly the thai food places in Thai town (ruen pair is my fave... but its closed for renovations).
I LOVE Indian/pakistani, and I think Al-Noor in Lawndale definetly fits the bill for spicy. It's VERY spicy if you want it. Also right off the 405, well priced, and oh so delicous.
get the tikka massala (chicken or paneer), naan, and rice.
My vote is for Indian as some places will crank up the heat to eye watering, mouth burning hotness (upon request).
Example: Bombay Cafe, which I haven't been to in a few years, had a briased Lamb Frankie that they used to offer on a hotness scale of 1 to 10. An 8 was enough to bring tears to my eyes. Also, Akbar has on the Lunch specials menu each item listed on a hotness scale of 1 to 5; the 5 is fairly intenese.
Indian Restaurants in L.A. - There is most excellent post by "losfelizhound" in the link below to find the best spot nearest to you: