Wouldn't leave him negative but to the lenders: you should make it clear in your feedback that he was late and that he used the money for gambling. That's important.
The coins that I gambled were not mine but of a friend whose things were sold by me, like Gift cards, Bitgold, etc...
Sorry bro, that doesn't make sense to me and seems shady as fuck, to say the least. In all honesty it sounds like something a degenerate gambler would say. You borrowed money. You're late. You're laying bets. What do you expect the community to think?