I walked into the employee's entrance of my building and the security guard said: "Visitors must use the main entrance."
So I had to walk around to the front, trade my (deactivated) employee badge for a visitor's badge, and then walk up to my office to clear out my personal effects - for which the cleaning guy had thoughtfully left a couple black plastic trash bags.
More here. Fortunately, all my horror stories are about the actual work, not the firing.