What's the worst thing you have done to another person to get ahead in your life?

I haven't done anything myself because I have never been the type of person who has wanted to climb any sort of social/corporate ladder (still have time though; I'm only 20). I do, however, have a story from High School when someone tried to get ahead at my expense.

It was my freshman year and football tryouts had recently begun. In Junior High we had multiple teams; so with only one team this year we were just figuring out everyone's skill levels. One of the kids was worried about how good I was at my position...and so was his over protective father. They somehow figured out that I wasn't living in the school zone and was using a friends address in order to attend our school (used to live within the school zone and didn't want to switch schools when I moved). The kids father called my house and threatened me (a 14 year old kid) saying he would tell the school board and not only get me kicked off the team but force me to switch schools. I called his bluff and he turned me in. Luckily we found a loophole; having a P.O. Box within the school zone counted. Both the other kid and I ended up starting anyways; he at right guard and myself at left.

So Reddit, what's the worst you have done to another in order to get ahead?