What are some embarrassing mistakes foreigners make in Thailand that others should avoid?

Sounds like you've been around the block Sophie 👍 and for the ladies playing along at home... females are not permitted to touch monks. If an exchange of item or offering is to occur, it is typically placed on a cloth and gathered by the monk, never directly hand to hand. Good lessons. TY Sophie 🙏

Many years ago my wife got annoyed with me about, I still don't know what, but she through me out of the house. In those days 30mins out of BKK not too many ppl spoke good English. So I caught a tuk tuk into Patpong where I knew ppl spoke good English. I walked into The Rose Hotel (I think it's still there) I said I'd like to book a room for 3nights pls... she said 3 nights, yes pls 3nights. She stared at me blank faced and burst into laughter. I didn't know what she was laughing at. She turned around to a room full of colleagues and spoke a few words in Thai which brought on laughter from the entire staff in unison filling the foyer with a chorus which brought back memories I had as a child in church at Sunday bible studies. I was fuming and so embarrassed and I still didn't know why. So after my PTSD was triggered the room fell to a deafaning silence. She then calmly explained to me... Sir, this is Patpong... nobody has ever asked for a booking longer than three hours. You can book for 1hr, 2hr or 3hr, no more she said. At that moment it dawned on me why everybody was laughing at me. I didn't have to speak Thai to now know what she told her colleagues. I was so embarrassed. Well, it's something I can laugh about in my older years i guess. 555

I was stopped on a motorcycle in pattaya to be fined for riding three persons on the bike. The motorcycle that pulled me up had five cops on their bike... go figure 🤷

When I was new in Thailand and didn't speak Thai too well (about 1990) I made a huge embarrassment of myself...

The Thai word for luggage is 'Gabouw' the Thai word for scrotum is 'Gaborg' ... we were at BKK airport with the family and others... my Thai mother in-law was maybe mid 60's. We were about to travel international, mother and I waited together, bags on floor while everybody did some shopping. Shopping done, Everybody returned and we were off to board the flight. Everyone started to pick-up their bags... I said in Thai to mother... no, no Ma... dont worry I'll carry your Gaborg. How embarrassing everybody in earshot just started laughing so loud, even strangers nearby started laughing at me, then it seemed like the whole terminal was laughing at me... I had told my mother in-law that I would carry her scrotum for her. Gulp!, I was left very red faced and very embarrassed. Oh well, you live and you learn. Well, most of us.