The principle of charity is basically you assume your opponent's ideas, claims, arguments deserve merit and a charitable assessment and thus you address them with a courteous disposition. This is employed commonly in philosophical discussions in controversial topics but applies just as well in other areas. However, this principle works only so far as the warrant of the arguer's assumption of his/her opponents disposition to want to listen and be argued with. If you sense and know your opponent is just being a troll and condescending, you have no obligation to employ said principle. Hence, Jesus' claim recorded on Matthew 7:6.
