One situation i liked to make a joke with my GF. I called her at Valentines day, knowing that she was waiting for it for sure. I did like i would have forgotten that day.
Me: Hi Tilak
She: Hallo Tilak how are you, bla bla
After a time she asked me "Tilak do you know what day?"
As i was online i just opened the thai Phrase book and looked for the Thai Word of that day
Me: Sure tilak, today is tuesday(in Thai) "
this was the point when the line got very quite. Suddenly i realized that the joke failed and the trouble was coming up. It took me long time to make her sure i didnt forget that day. And this was not the only joke wich went into a disaster.