Q: My husband's ex asked me what we bought their son for Christmas. Because he and his dad love baseball, I told her we bought him a jersey and tickets to a game when their team comes into town. She has remarried and celebrates Hanukkah with her new husband and wanted her son to participate in the first night. We thought that was great. Hanukkah was last week, and she bought him the exact jersey we bought him. I think she did it on purpose! My husband doesn't think so. I'm furious. What's good ex-etiquette?

A: I've worked with quite a few new partners who feel as if the ex has ulterior motives. They believe they want to screw things up in some way — "They don't want us to be happy," or "They want the children to like them more." All that makes them do underhanded nasty stuff like buy the same present as you bought and give it to the child first — and you're the victim to all their passive-aggressive behavior.

I'm not saying any of it isn't true. As I said, I've counseled quite a few who are convinced their partner's ex is out to upset their applecart, but I will tell you what I tell them.

Do you want the kids in your care to flourish because of you or in spite of you? Most say, "because of me." Then, act like it.

It's not you against them. It's everyone (mom, dad, new partners, friends who support your effort, extended family, everyone) for the kids in your care. If you spend all your time trying to one up each other, no one will ever win, and the kids will definitely lose. The model you're giving them for adult relationships — the people who are supposed to be taking care of them and teaching them to be loving, productive individuals — is competition, lying, passive-aggressive nonsense.

I'm not saying you're right and mom's behavior is all planned. It makes no difference if it's true — you think it is, so you're responding in kind. Don't be swayed by what you perceive as another's bad behavior. Be the person you want to be, and you'll set the stage for the rest of the players. They'll see it and follow. It may not happen immediately but it will happen — every family needs a hero.

The question now is how do you discuss this with the other home without perpetuating the passive-aggressive stuff and set an example for working together in the future?

Good ex-etiquette for parents Rule 8 is "Be honest and straightforward." I'm not sure how active you are in the co-parenting and it may be more appropriate that dad say something rather than you, but the message is the same: "It's great that you supported the same theme for Jason's holiday this year, but the jersey you bought is the same one we had planned to give him. In the future, let's talk and plan together a little closer so we can give him the special holiday he deserves." Then elaborate, "Next year, what do you think about …?" That's setting the stage to work together in the future — and, that's good ex-etiquette.

Jann Blackstone is the founder of bonusfamilies.com.