based on the phrase "Jumping the shark".
Used to describe a person who at one time may have been seen in a favorable light - and is now unfavorable to be around.
At one time, said individual's shortcomings may have been tolerable, overshadowed by their good qualities - now the individual has become intolerable and brutal to be in the company of.
John officially became a shark jumper when he stopped pitching in for gas money
You became a shark jumper 5 monutes after I met you.
Everyone loved Taniya when she came to town, I could tell she was a shark jumper from the get-go.