Here is an example illustrated with a photograph from Joe Six-Pack’s Gearhead Catechism™.
The late Fr. John Hardon, SJ, explains it well in his Modern Catholic Dictionary,
OCCASION OF SIN. Any person, place, or thing that of its nature or because of human frailty can lead one to do wrong, thereby committing sin. If the danger is certain and probable, the occasion is proximate; if the danger is slight, the occasion becomes remote. It is voluntary if it can easily be avoided. There is no obligation to avoid a remote occasion unless there is probable danger of its becoming proximate. There is a positive obligation to avoid a voluntary proximate occasion of sin even though the occasion of evildoing is due only to human weakness.
Proximate = Near. *burp*
Bonus entry: Did the driver of the white Dodge commit a sin?
Certainly. The photograph above nicely illustrates an example of a sin against charity. I mean, if you truly love your neighbor as yourself, why would you park your car in someone else’s space like this? By doing so, you may lead your neighbor to a place where bad things can happen to both of you. This is A) why we can’t have nice things, B) why there is such a thing as Just War (waged by clients of auto insurance companies), and C) why personal sin is actually societal in its effect.
Moral: be mindful of your neighbor in parking lots. By doing so, you will be blessed.