I remembered an incident from school – I was talking to a classmate, and he asked me something, and I replied, "I have no idea." Then, a strict teacher walked by, and they dragged me to the principal's office, where I managed to explain myself. It was an English-language school, and I simply inserted an English word into my speech, like "Who knows," and they thought something else, showing that their minds were in the gutter.
Awesome! That's how you showed them what they were thinking.