Open your mind a little and it's easy to think of many ways this could be used without offending. My girlfriend and I jest with each other. Either of us could say it and both laugh about it. There's a waitress in my building I can jest with as well, or if she were complaining to me about another customer I could quietly tell her to go give them a knuckle sandwich. We would both laugh. Nobody is offended. If I heard the term on an old Thai movie, or used by another person, in jest or otherwise, I would like to be familiar with the term and know what they said. Why do you assume the OP is going to go out and start threatening random people with a knuckle sandwich? Seems like a simple, straightforward question to me.
My Thai is pretty good, but I had no idea how to say 'knuckle sandwich'. I find it both informative and entertaining. Are you here to help or be a snob?
