Formal:
* ลาก่อน (laa-gawn) - This is the most formal way to say goodbye and is used in situations where you are speaking to someone older, of higher status, or someone you don't know well.
* สวัสดี (sa-wat-dee) - Although it literally means "hello," it's also commonly used as a polite goodbye.
Informal:
* บ๊ายบาย (baii-bai) - This is the most common and informal way to say goodbye, similar to "bye-bye" in English. It's used among friends and family.
* เจอกันใหม่ (jəə-gan-mài) - This means "See you again" and is a common way to say goodbye, especially when you expect to see the person again soon.
* ไปแล้ว (bpai-lɛ́əw) - This literally means "I'm going now" and is a casual way to say goodbye.
Other useful expressions:
* ขอบคุณ (kɔɔp-khun) - Thank you.
* ขอให้โชคดี (kɔɔ-hâi-chôk-dee) - Good luck.
It's important to note that Thai people often use gestures along with their words when saying goodbye. A common gesture is a small wave of the hand or a slight nod of the head.
Remember, the most important thing is to be polite and respectful when saying goodbye in Thai.