It's wrong to cause someone to get a bad grade.
Sam's friend has an important test the next day that they haven't studied for yet.
Sam wants to go out drinking.
Sam leaves his friend to study for his test and finds some other people to go drinking with.
Sam insists that his friend go out drinking with him instead of studying for the test.
Sam's friend passes his test the following day and ends up passing the class.
Sam's friend fails his test and his grades drop as a result.