>>3 that you have a gay experience by incident, like you trip and fall on the mouth of someone of your sex with your mouth, or instead of mouth, sexual reproductive organs
That would be "accident", not "incident".
"By definition, an accident is unforeseen or unpredictable. It is something over which you have no control, and therefore it is unavoidable. An incident is simply an event or occurrence, whether it is predictable or not." ~Some unrelated website
But if you really want to know what Kinsey meant by the word, just Google "kinsey scale" and do some research.