Utensil-related issues
1) Do eat with your spoon and not your fork; the spoon in your right hand, fork is in your left. Use the fork to push food onto your spoon and put the spoon in your mouth. (TRE 2)
Although it’s not absolutely wrong to stab your fork into the middle of meatball and eat it right off the fork, it’s too tacky to do at a formal dinner. It’s shows an obvious lack of table manners at the same level as putting a knife in your mouth would be for Europeans. The Thais would hold the meatball down with their fork (because the meatball might bounce out of the plate when you try to cut it) while using the side of their spoon to cut the meatball to a bite size, and then would scoop the bite-sized chunk of meatball in the spoon, then eat off the spoon.
Thais mainly eat everything with a fork and spoon. When you go to the countryside, they might give you just a spoon–a short one too!