In the first episode of Season 2, Jimmy and Kim decide to scam a stockbroker they meet in the hotel Jimmy's staying at. After hearing the obnoxious man on the phone, Jimmy begins to circle his prey, with him and Kim pretending to be a brother and sister who don't know what to do with a large inheritance. Ken offers some advice, and buys a very expensive bottle of tequila. They leave him thinking he's won a lucrative contract, but all he's got is a huge bar tab to pick up.
You might feel some sympathy for Ken, until you remember that he's a massive a**hole. He initially appeared in the first season of Breaking Bad, in the episode Cancer Man. He steals Walt's parking space, and then loudly talks on his bluetooth headset, completely ignoring Walt. Later, when Walt recognises his car, he puts a squeegee between the battery terminals, causing it to explode. Ken's suitably shocked and angry, though you don't care, and Walt takes a tentative step to becoming Heisenberg.