Had a similar event when I was a PhD student - got invited out for a drink with an old school mate working in the finance sector.
As you know PhD students aren't exactly raking it in - ate dinner at home, got a $50 out which I figured would be good for a few rounds of drinks with a mate and caught the train in to meet him outside his office.
He rolled out of the office with some office friends, we introduced around and they all decided they were going out for dinner - friend hadn't eaten, we should go too. I said I had eaten but I was happy to tag along if that's what he wanted to do. We went to a relatively swanky place ~ $30-40 a main. I order a domestic beer, while the finance guys order up a couple of bottles of wine and a round of oysters, from which I refrain. They order up mains, more wine, and round it off with a round of after dinner scotches.
As we're starting to get ready to leave, I ask the waiter for my bill separate, which brings the table to silence. One of the guys I just met says "Ahh mate, we're splitting it even." Admittedly I had a glass of wine when it was offered, but aside from that I had consumed two beers. I reply - "If you guys want to split it amongst yourselves, that's fine, but I didn't eat so, I'll pay my own bill." To which my mate says "Come on, don't be a tightarse." I told him rather loudly that I thought trying to make a uni student on a scholarship pay for your oysters and 21 year old Glenfiddich when was being a tightarse, paid my bill and since I moved interstate then overseas, I don't think we've spoken since.