I remember the skint days at my first job after uni, when I would on rare occasion go to dinner with a bunch of (mostly) CFs who would order from soup to nuts, while I carefully selected my dinner and kept an eye on my wine consumption...and then, of course, it would be "let's just split it." GRRRRR. These days, I tend to overpay, as I will have an extra glass of wine, but the attitude now is "oh, it doesn't really matter" -- however, I remember the old days and insist on paying more.
Two stories from uni days, and I believe the first on this thread to involve, um, illicit substances. My roommate had loaned her CFBF $40. He paid her back with 20 purple microdots, for which he paid $10, but she could sell them for $2 each. I pointed out that he had not repaid her in full, as she would be doing the (illegal) work to make up the difference, which was really his job. She refused to see my point (and not because of the PMDs), and went and earned the $40 he owed her.
Then, at a party, a CFF of mine asked me quietly, "Hey, you wanna go do some blow?" I agreed, followed her into a private room, and waited. She giggled, and said, oh, I don't have any, I thought we could do yours. (assuming I had some).
The only other CF stories I have involve rude relatives, usually after another relative has passed and they turn into vultures, but I'm sure most of us have similar stories. Otherwise, I'm lucky to have little to no interaction with CFs, and would swat them down if I did. Hope I didn't offend with the stories from uni, but those were different times, and my only vices these days are wine and cognac!