Examples of foreshadowing include a teenage guy about to leave the house for a night out with his pals, telling his mother that she worries about him too much, kissing her just before he goes. The reader is perfectly aware that something awful is about to happen, which is what makes this foreshadowing: providing clues about something bad that is on its way, inevitably so.
In F. Scott Fitzgerald's classic novel "The Great Gatsby," when Gatsby, Nick, Tom and Daisy all head into New York City for an ill-advised spree in a hotel suite on one of the hottest days of the year, it is clear that bad things are on the way. First of all, as they drive into the city, they stop at George Wilson's garage, where Tom's mistress (and George's wife) lives. She is nowhere to be found, though, and George indicates that the two of them are about to move away. Nick looks up to see her locked upstairs; the upshot is that Tom's affair is just about over. The menacing tone at this point in the story only worsens as the party of four becomes a brutal confrontation, and when the party breaks up (with all intoxicated), Daisy ends up accidentally running George's wife down in the road on the way back, as George's wife had seen the car and thought it was Tom coming for her.