This trope is situation where someone becomes a tempting target which others will try to take direct advantage of. This is usually through some quality of theirs.
Generally comes in three general flavors.
Type I - Taking advantage of someone else's good fortune.
Lets say Bob becomes wealthy. Hearing this, Alice, an acquaintance of Bob presents him with an investment opportunity, that can't possibly fail. Or maybe she announces that she's a long-lost relative of Bob, and if he could just help her out a little financially, she'd be eternally grateful. In general Alice wants to profit off Bob's wealth.
Another case is where Alice becomes famous, and Bob offers to become her publicity manager. He's offering not because he's experienced at this type of work, but because he can profit off of her publicity.
Type II - Being in the wrong place at the wrong time.
An example is Bob who doesn't have any street smarts. He's walking down the street in the wrong neighborhood, and is spotted by Alice, who sees him as an easy mark.
Bob has just come into some money, a lot of money. Maybe he won the lotto, maybe just got an inheritance, but he feels the need to tell anyone and everyone about it. Or maybe he just flashes his money around in public. Charlie sees this, and thinks he could part Bob from his money rather easily.
- In the Futurama episode, My Three Suns, Fry drinks the former emperor of a planet of liquid-like beings, becoming the new emperor himself. This makes him the target of assassination. Subverted, in the fact, not being liquid himself, he's immune to their attempts.
- An episode of My Hero where George has won the lottery has a gag where he says a lot of long lost cousins have been turning up.
- An episode of DuckTales, Til Nephews Do Us Part has a Millionara Vanderbuck trying to marry Scrooge for his money.
- In the Kim Possible episode Ron Millionaire, Ron Stoppable becomes wealthy, and acquires several hangers-on including Bonnie. He's later kidnapped by Dr. Drakken and Shego, and forced to finance their latest evil scheme.
- One time on Life Crews & Reese investigated a group of people all of whom had won the lottery; the richest person in the group had won like $100,000,000 and had turned his house into a bunker because of all the people coming to him for handouts, etc.
- Thomas And Martha Wayne were gunned down in an alley. This isn't quite the trope, as at the time the place was known as a nice neighborhood. However, since then its become known as Crime Alley, and is now definitely this trope.
- In the Master Keaton episode Love In May has a Japanese tourist have her purse and luggage snatched. She's targeted because she was old and a tourist.
- In Buffy the Vampire Slayer, the alleyway behind/beside the Bronze (it's not really clear on its placement) is this with a twist. You're not likely to get mugged, you're likely to be an unwilling blood donor of the neck bite variety. It's also one of Buffy's primary hunting grounds, such that one wonders why vamps still try killing people there when they know that there must be a thick layer of dust from how many of their kind have died at the Slayer's hands back there.
- In Donald E. Westlake's novel God Save the Mark, the hero is such a sucker that con artists from all over the city practically line up for the opportunity to take his money.
- On The Beverly Hillbillies Mr. Drysdale was always on the lookout for these, because Jed & clan were too trusting to believe that anybody was trying to sucker them.
- William Shakespeare's Timon of Athens falls under Type III: He's rich and so trusting that a bunch of sycophants gather around him, waiting for handouts.
- In Better Call Saul flashbacks show that Jimmy's father was an extremely easy mark. He would always take people at their word and would give money to anyone who came in with a sad story. The one person he did not believe was Jimmy who tried to tell his father that he was taken advantage of. In one instance a conman blatantly confessed to Jimmy just out of the father's earshot and the father still took the conman's word over Jimmy's. This caused Jimmy to develop contempt for his father and he became a conman and thief himself. In the end Jimmy's father had to close down his store and died broke.