The phrase "messing with" is a colloquial expression that can be interpreted in various ways, including teasing, bothering, meddling, or fooling around. Some synonyms for "messing with" could be: teasing, playing with, annoying, interfering, meddling, toying with, getting involved, fooling around, disturbing, meddling, or tampering. Depending on the context, one synonym may be more appropriate than the others. For example, "teasing" may be used when playing around with a friend, while "meddling" may be used when referring to someone who is getting too involved in someone else's business. Overall, it is essential to consider the context and the intended meaning when looking for synonyms for "messing with".