Mixing it up with someone implies associating or engaging in social interaction with them. However, there are times when we may want to distance ourselves from specific individuals or groups. In such cases, we can look for antonyms for "mix it up with." Some possible antonyms include avoid, ignore, shun, ostracize, or isolate. These words convey a sense of intentional detachment or isolation from others. They suggest a desire to disengage from social situations or certain individuals, either due to personal preference or a need to protect oneself. Therefore, depending on the context, using these antonyms is one way to indicate a reluctance to socialize with someone.