Ex is being unreasonable about summer schedule

So my ex wants to switch our summer custody arrangement last minute because her boyfriend got tickets to some concert. We already agreed on the schedule back in March. My kids are signed up for baseball camp the weeks she's asking for. I told her no but now she's threatening to take me back to court over something completely unrelated just to pressure me. Is this normal? How do I handle this without it blowing up in my face?