Alienate the Kids
It is hard to speak positively about someone that you are fighting with. If this is the case for you, the best thing to do, especially if the other parent is speaking poorly of you, is to NOT return the favor. With both of you saying bad things about the other, the kids are going to feel the need to pick sides and will get caught in the middle. Bite your tongue if the kids start reporting bad things your ex is saying about you and focus on being the best parent you can be instead. Actions speak louder than words.
Emotions are very high at this point in your life. I understand that all too well. Especially if you are the father, your yelling will be perceived as aggression. When a man yells at a woman in the middle of a custody dispute, the woman is likely to claim that she fears for herself and the children. You are clearly aggressive and unable to control your temper. Assume that every conversation you are having is being recorded because it just might be. It is extremely easy to record telephone conversations today and, with cell phones, it is just as easy for the other parent to click record and put the recording cell phone in their purse or shirt pocket and record your ranting. If they know the conversation is being recorded, they will not yell back and may end up looking like a victim and that makes you look like the criminal.
Fight or Get Physical
Do not heed the words of Olivia Newton John and "get physical". While your temper may be at a boiling point, it is NEVER advisable to physically harm another person, especially the other parent. If the other parent gets physical with you by pushing, hitting or shoving, do not return the favor. Leave the situation (hopefully with your children) and call the police to file a report. An order of protection or restraining order may also be advisable. Contact an attorney before taking any legal actions, though.
Move in with your boyfriend or girlfriend
Typically, moving a relationship to the next level is a good thing and I congratulate you for moving on and finding someone special. In the middle of a custody battle, however, you need to show the judge stability. In the middle of a divorce, or even shortly after a divorce, your children are still adjusting to the massive change of divorce and it is not the time for yet another change to be heaped upon them. If you have been divorced for a while or you were never married, it is still not a good time to move someone in to the children's lives. The custody battle requires that you show the judge that your home is a safe, stable environment for the children. Adding another person into the mix does not add stability.
Criticize the other parent to other adults
You were a couple and now you are not but it is highly likely that you had mutual friends. Even if you don't think you had mutual friends, keep in mind that your friends are going to talk, too, and their friends may be friends of your ex. Assume that everything you say is going to be reported back to your ex. If your ex is engaging in risky behavior like drugs, drunk driving or other things that may endanger your children, you will need to talk to an attorney and take more drastic action. Talking to your friends is not going to fix the problem in this situation, either.
Stop paying child support
Failure to pay support obligations can result in jail time and it is very difficult to see the kids from behind bars. Do almost anything to make sure that your support obligations are being met. Parenthood is not a pay-to-play event. You get to be a parent whether you pay or not. Failure to pay, however, can be seen as contempt of the court's orders and potentially as financial abuse if you have the ability to pay.
Damage someone's property
I'm sure it would feel so vindicating to slash the other parent's tires or key your in-laws' car in the middle of the night but resist the urge. While it is a big leap to go from keying a car to hurting your children, judges have amazing legs and can make some pretty big jumps. It's best to take the ball away from the judge and your ex and take the high road. You don't want to be perceived as an aggressive, dangerous person.
Deny the other parent telephone contact
This is similar to alienation of affection but more subtle. When you deny the other parent access to the children, whether it is physically denying them access or merely denying them telephone calls with the kids, you send a silent signal...the other parent doesn't care. You will not get away with it. If the other parent is trying to contact the children, let them speak. The other parent will be keeping track of the times you refused access and tell the judge that you are interfering with the parent-child relationship. In the short term, the kids will think you love them more because you obviously are calling them every night and the other parent can't be bothered. In the long run, though, you will be painted as someone who does not value the other parent and the children's need to have both a mother and a father who love them.
Go on an unexpected vacation
The kids will be so surprised if you take them to Disneyland for a week. They will be so happy. The other parent, however, may assume that you are kidnapping the children and may be inclined to get emergency orders for you to return the children immediately. The golden rule of "do unto others and you would have them do unto you" applies here. You would be upset if the other parent up and skipped town with the kids so don't do it to the other parent. Provide the other parent with a complete itinerary of the trip as far in advance as possible. Include trip times, where you will be staying and how to reach you during your vacation. Of course, I wouldn't be an attorney if I didn't tell you to give notice in writing. Email is fine.
Take the kids out of school or daycare without notification
If you showed up to pick up your children from school and they were not there, how would you react? I would absolutely lose it and think that someone had abducted my child. Police would be called and local news helicopters would be circling the area looking for the abductor of my beloved child. They would all be looking for YOU. Don't do it. If you are going to take the kids out of school unexpectedly, inform the other parent or wait for Chopper 5 to be circling over your house looking for little Bobby.