I don't mind buying anyone a drink, I don't keep count, over time I thinks it's swings and roundabouts and it all works out.
However I can't abide people who avoid their round or those who have schemes to avoid paying their way, like offering when everyone else has a full glass or at the end of the evening when no one wants more.
I'd absolutely hate to be someone who didn't pay their way. If I can't afford to buy a round, I wouldn't go or wouldn't accept offers/get involved in a round.
It doesn't seem to be people who are hard up either, they have money to spend on other things.
So why do they do it, just pure brass balls and because they can or is there something else?