There are several synonyms for the phrase "make unfriendly." Words like alienate, estrange, distance, and isolate all convey the concept of causing a rift or a lack of warmth in a relationship. To alienate someone means to push them away or cause them to feel unwanted, while to estrange implies a separation or distance between two parties. "Distance" can be used to describe a physical or emotional gap between individuals. Lastly, "isolate" is a more severe version of these words, implying a complete removal or shunning of the person. However, it is essential to remember that making someone unfriendly should be a last resort, as it can have long-lasting negative effects on any relationship.