A woman I know is notorious for offering to meet someone for an errand or lunch or something and "forgetting" her wallet -- leaving whatever sucker... um, friend - I meant friend, yeah -- to pay for HER lunch, HER errand purchases, and even HER parking fee!!
Eventually (like, months later, after several reminders) she will reimburse for the errands and parking -- but figures lunch was a "treat" -- after all, you had the pleasure of her company!
I don't meet her for lunch or anything anymore and haven't for years. Can't afford it!