As much as I hate all of those, they can't compare to a reprehensible technique I recently experienced: the salesperson end run around IT.
Here's how it works: The vendor's salesperson doesn't like the answer IT is giving him. That's normal; salespeople don't like to be told no. But the salesperson then goes to the CFO and tries to convince financial leadership that IT leadership is squandering the budget.
Here's the email that the salesman in question sent to the CFO of Beth Israel Deaconess Medical Center. The salesman's name, along with a few other identifying bits, has been redacted, though I'm not sure why I want to protect the identity of this weasel.
"From: Sales Specialist at a large vendor
Sent: Wednesday, March 28, 2012 9:00 AM