When northern people came to the south to take advantage of their poor situation when they were vulnerable. This was after the Civil War and people were upset about it.
There is a modern day version which does not occur too much. See example for more.
Hillary Clinton. She came to New York from out of state, not knowing much. Bill tried to be cool and get an office in Harlem, but not one person bought that and saw through his attempts to conceal his non-new yorker self. You can't just go to another place and act like you own it. Con artists are good at this, and that is how she won.
For years, and even today, (real) New Yorkers have held signs and had bumper stickers saying things such as "Hillary GO HOME"
It is commonly understood that Hillary Clinton is not a New Yorker. However, it is equally understood that as she changes her mind on issues in a matter of minutes or depending on the audience, that she may change who she is (for example: saying she is from New York to New Yorkers, when she really is not. She could learn some lessons from Obama (a real democrat) who is consistent and does not tell lies.
What made hillary a Carpetbagger?: she took advantage of New York and her fame and ran for Senator. She was elected after her strong opposition was diagnosed with prostate cancer and was forced to drop from the race. After she was elected, it was clear she had no real interest in New York, and she was going to simply use it to run for President down the line. She knew it was impossible to beat President Bush in 2004, so she waited until now, and here she is. If she was serious about New York, she would do more than vote for $1 million in Tax funds for the hippie Woodstock concert museum, but the majority of New York's fire and ambulance services are volunteer and don't have enough federal funding. This shows her lack of genuine interest in New York.