Although jmat's description of event and occasion are correct, I think that he has reversed the meanings of incident and accident. Perhaps because he has confused 'an accident' with 'by accident'. Although 'by accident' can be 'not a bad thing' - 'an accident' would always be a bad thing, involving hurt or damage. Conversely, an 'incident' is an unusual (and usually substantial) occurrence that does not have to be a bad thing. Something like a dog running onto an airport runway would be an incident. A plane might have to abort a landing, the fire trucks might be deployed. It would still be an incident, even though nothing got damaged. There is not necessarily any ill-intent in an incident either.

An event is something that happens. For example, writing this message is an event. An occasion is a more important event. For example, a meeting or date can be considered occasions. An accident is an unintended event. For example, finding money on the ground or slipping in mid are accidents. Note that an accident isn't always a bad thing. An incident, however, IS a bad thing. Slipping in mud, cutting my finger etc. It doesn't have to be accidental, but if it wasn't it implies someone else had ill intent.

"accident" referring to disaster, calamity, or havoc.. "incident" referring to danger, or peril.. "event" referring to show and "occasion" referring to ceremonial things, etc