Formal:
* ขอบคุณ (Khop khun) - This is the most common and polite way to say thank you. It is used for all situations where respect is required.
* ขอบคุณมาก (Khop khun maak) - This means "thank you very much" and is used for expressing greater gratitude.
Informal:
* ขอบคุณ (Khop khun) - This is still polite but slightly more casual.
* ขอบใจ (Khop jai) - This is the most informal way to say thank you. It is generally used with friends and family.
* ขอบคุณนะ (Khop khun na) - This is also informal and adds a friendly touch.
Note:
* The tone of voice is important in Thai. You should speak softly and politely when saying "thank you".
* It is customary to add "ka" (for women) or "krap" (for men) after any polite phrase, including "thank you".
Let me know if you'd like to learn more about Thai language or culture!