As far as I can gather from my Thai lawyer friends and google searches, carrying any kind of knife (farm workers excepted) is illegal.
But you can see many people with knives in their pockets (by the pocket clip showing), and I’ve seen bus boys with swords down their pant legs and others with guns stuck in their belt.
So, I think you’re OK with a small folding pocket knife. Use it as intended, only when needed, and be mindful of your surroundings.
Unless your in a tourist trap area where cops might look for targets you should be fine.