Sun opposite Mercury transit has a stimulating effect on mental activity. Your interactions with other people are brought into focus. Your thinking is not in balance with your goals and your ego, conflict and arguments could result if you push too hard because you are likely to speak without thinking and stir up opposition.
You are thinking more about yourself and your own views are likely to be narrow, and this is what causes others to get their backs up. The key to handling this difficult energy is to listen more than talk and remember to think twice before making statements or expressing personal opinions that might offend.
This is not the best time for asking for a raise from the boss or trying to reach some deal in business. Things will go easier if you keep selfish thoughts to yourself. Make a conscious effort to give some ground in any arguments, at least till a more favorable time when your thinking is more balanced.
This interpretation for Sun opposite Mercury transit can also be read for a Solar Eclipse and New Moon opposite Mercury.