Yesterday I had cause to tell a Thai they had "pissed on the chips". The phrase went completely over the head of the Thai and I got the blank stare, which is partly what I was aiming for (didn't want them to fully understand how angry I was).
I've also said to a Thai "why would I have a dog and bark myself". Translated into Thai that's actually fairly rude.
Have you ever had cause to use an English [language] phrase that's completely lost on your Thai counter-part?