If you overstep the mark, you offend people by doing something that is considered to be rude or unacceptable. They agreed that by criticising his manager so publicly, Taylor had overstepped the mark. Sometimes newspapers overstep the mark but overall they do more good than harm. Note: The `mark' in this expression may be the line behind which runners stand before the race. Alternatively, it may refer to boxing matches in the past, when a line was drawn in the ground which neither boxer could cross.