Sometimes we run into a player that is not completely honorable. If you are in a game and a player does something not right or honorable, take a screenshot. Its easy.
Hit the Print Screen button at the top of your keyboard. Then, bring up the paint program.
Click on edit.
Then, click on paste.
Then save it with a name.
Keep your powder dry! Don't post your screen shot right away. Let the offender lie, then post your screenshot. It makes it more effective.