A Spencer
A Spencer is the kind of guy who'll listen to your problems for years, then copy your bet and let you lose everything. He's like a dog who follows you everywhere but still steals your food.
Spencer: 'I'll bet with you, but only if the odds are good.'
Spencer: 'You lost your money? That's your own fault.'
Spencer: 'I'm just like a dog, I follow you, but I still steal your food.'