Who's your worst Sales colleague ever?

We've all had colleagues lie, cheat, steal deals, suck up to terrible bosses, drop the ball and ruin deals for you, but who was the worst?

I actually had a colleague selling a different product call into my customer's boss THE DAY AFTER HE SIGNED A CONTRACT to tell him he "bought the wrong thing." Cut to my customer calling me he now "looks like an asshole," and I had to get multiple management layers involved to tell my colleague to back the F off. He didn't get fired just then, but he did a few months later for underperformance.