The correct answer is C. annoy him.
To rub someone the wrong way means to say or do something that upsets or offends them. If you annoy someone, you make them feel irritated or frustrated. This can be done by saying or doing something that is rude, inconsiderate, or simply not to their liking.
Flatter someone means to praise them in an excessive or insincere way. Encourage someone means to give them support or confidence. Abuse someone means to treat them cruelly or violently.
In this case, the speaker is warning the listener not to say or do anything that might upset or offend the person they are talking about. The speaker is saying that if the listener does something to annoy the person, they are likely to react in a negative way.