The phrase "mix it up with" typically means to engage in a disagreement or altercation with someone. However, there are many antonyms that imply peaceful resolution and harmony. Some of these antonyms include reconciling, harmonizing, cooperating, collaborating, compromising, empathizing, and forgiving. It is important to remember that conflict can often be avoided or resolved through effective communication and understanding of different perspectives. Rather than "mixing it up with" someone, strive for peaceful and respectful interactions to foster healthy relationships and environments.