Poltergeist? Teenagers are more likely to have them...
A loose wire somewhere... evidently in the switch mechanism.
I had my fan turned on and then turned off by a spirit; I could see the outline of what looked like a person bending down and turning the knob; but this was no person; I was able to verify that.
You didn't have it turned off well and the button just popped back in enough to make contact.
sun spots or you been drinking again?