1. I’ll get you out of trouble this one time, but don’t ask me to do it again. It goes against the grain for me to help you when you should take responsibility for your own actions.
2. Terry noticed that the cashier in the store had given him too much change, and he went back immediately to return it. It would have gone against the grain for Terry to keep the money.

The expression originates from the idea that sawing wood against the grain (the natural direction of wood growth) is difficult.