What if they insult me after I just complimented them? How can I show them I don't feel offended?

Changing relationships is rarely done in a single exchange of words. Usually, the more persistent party will prevail! Showing them you don't feel offended keeps the game going, but you want to end it. Try leaving it be, don't conceal your disappointment, and work over that most insults are based on the offender's own insecurity. Next time you meet, continue to be the mature one. Persist and win, or if it does not work even after multiple tries, then confront them in a non-aggressive, solution-oriented way. If they persist in negative behavior even after this, take it up a level: involve authority. At last, if that is not an option, walk away.