I'm curious about any foods that I should avoid in Thailand. Are there any dishes or ingredients that might be problematic for foreigners?

Make sure it's cooked before you eat it, if in doubt leave it out, 7/11 will not let you down, 

Somtam with raw crab.

 

Raw/live shrimps

 

The cooked/prepared "Kanom Cheen' and 'Ahahn Damsan' dishes you often see in food courts and street markets, where it's cooked in the morning and served all day from unheated, fly-blown displays.  Only eat this when it's first put on display, never at the end if the day.

 

Khao Soi Ghai if wearing a white shirt.

 

Anything a Thai person says is "quite spicy'.

 

Pizza with tomato sauce (it's just wrong).

Stay away from raw seafood and home made fish sauces that may cause liver flukes and lead to liver cancer.  You'll see it a lot on street kiosks, including raw crabs that are used to flavor local treats.

 

Locals and long stay folks go to the pharmacy and buy (over the counter, no script required) anti-parasitics and take it every so often as a precaution.  Albendazole and Praziquantel are examples, but do some searching to find out the upsides and the downsides.

 

Keep some Imodium around.

 

Ladyboy Sausages

5 minutes ago, Kinnock said:

Pizza with tomato sauce (it's just wrong).

 

I hope you're thinking pizza with ketchup, because that is a crime.  Pizza with tomato sauce can be quite good.  My favorite, though, was Scoozi smoked salmon pizza.  (Shameless plug for Scoozi, but I like their pies)