Similar story. Everyone must say "Hello" or "Good Morning" to the receptionist in my office. She is rarely at her desk because she will find any excuse to not do her job so sometimes I don't even see her until after lunch time.

One morning I was on a pretty important call as I entered the office so I didn't say anything to her. She was playing Candy Crush, so I figured that she wouldn't mind. That afternoon my mail was unceremoniously thrown over the wall of my cubicle by her. One of my cubicle mates told me that I had better make it a point to say "Goodbye" on my way out and not miss another greeting or things would probably escalate. Apparently in the past she had dumped someone's garbage can on their desk after work, because that person had disrespected her by not greeting her multiple times.

I should mention that she is in her 60's. She was already fired from another department for spitting in someone's face, but was rehired and moved after she threatened a lawsuit. She also has gotten our office banned from multiple delivery places nearby due to her tendency to eat her entire lunch, find some minor fault, then call to demand a refund.