You accidently spilled coffee on a friend’s laptop. It’s not working now but your friend says you don’t need to worry about it. Use one of the phrases: on [someone’s] part, on [someone], on the off chance
You are late to a date because you had to take a bus, which you hadn’t planned. Use one of the phrases: on [someone], on the bright side, on the fence
A friend can’t decide if they want to go to a concert or not. You want to go with her. Use one of the phrases: on [someone], on the bright side, on the fence