I don't even know what to call behavior like this...

I’m not sure what to call this person. Inconsiderate? An opportunist? Self-centered? I dunno. I’ll relate the story and you tell me. A few years ago I was working at a software company. There were two secretaries there who, by chance, happened to quit at about the same time. The other programmers and I decided that we should take the two of them out to lunch before their last day. Just a way of saying thanks for all the good work.
There were about eight of us altogether, six programmers and the two secretaries. We ordered lunch and ate. Nothing out of the ordinary. Then the waitress came around and asked us if we would like any drinks. I myself do not normally drink during business hours. I said no thanks. A couple of the other programmers ordered beers. And the secretaries started in. They began to drink. And drink. And drink. I lost track of how many they ordered, but the number was considerable. It was enough that I remember wondering if they would be able to function at work that afternoon.
When they were done, the waitress brought around the check. The six of us each paid for our own meal, and we divided up the secretaries’ bill between us. I was unsurprised at that point to see that my share of their meals came to more than the entire cost of my own. Well, what could I do? I felt that they had perhaps taken unfair advantage of our offer, but I shrugged, paid the bill, and thought no more about it.
And then the kicker came. It turned out that one of the two secretaries had spoken with her boss early that morning and decided not to quit after all. She did not mention this when we offered to take them out to lunch for their last day.
So what’s the proper reaction? I was just floored. I was not and am not angry, just disbelieving. Is there a word for a person that pulls something like that? Or is it just me?

It’s a little more than inconsiderate.

I’d go with dishonest and no more dealings with her than necessary.

I’ve always liked shunning as a punishment.

Opportunistic leech seems to fit the bill. So does “low class swindler” and “biter of the hand that feeds her”. What a schmuck.

Okay, so it’s not just me.

Unfortunately shunning is no longer an option, as I don’t work there anymore. On the upside, that makes avoiding dealings with her quite easy.

She was out of line, that is certain. I am curious though, if you no longer work there and have no contact with this woman, why are you so upset? Your 6th of the bill which covered you and your part of 2 secretaries bills could not have been more than $25. In my opinon if you are upset about this very minimal cost, you should not agree to go to restaurants with your coworkers. She may seem petty, but you are even more so…

I’m going to have to disagree with you there, zwitterion. This wasn’t about the money; this was about misleading and taking advantage of co-workers, and behaving unbelievably inappropriately (the secretary, that is, not ForgottenLore). Letting someone else finance your piss-up on company time when you’re not actually leaving (but they think you are) is just…not done.

The incredibly tacky behaviour she exhibited is just the kind of thing that gets extra perks taken away from employees, and makes employees not want to do anything for each other.

Oh, I’m long past being upset. But it does still boggle my mind.