Letting him pay for all their expenses and not contributing even when they had funds. Actually they made some extravagant purchases and would then turn around and ask for help with some expense that came up.
Agreeing to do things on a certain date/time and leave him hanging/waiting for them when he was just there to help them out and they never showed or called etc.
The thing that bothered him most was that they never seemed to appreciate what he was doing for them, never said thank you. He didn't care about the money, it was the attitude.