It is critical that as a party in the case, whether you are the plaintiff or the defendant or a lawyer, you never, ever laugh or giggle in front of a jury. The moment you laugh during your trial and the jurors see this, you will automatically make it appear like you are not really the victim that should be compensated or awarded a verdict, that you are not taking the process seriously, and the trial is just a game to you. This applies to pretty much any type of civil (and criminal) case, including personal injury, employment, and medical malpractice cases. And even though judges are supposed to pay less attention to these types of things, I can't imagine how laughing would make a positive impression on a judge either (important in bench trials, when a single judge makes the decision on your case).
Being stoic or serious, both when you are on the stand and when you are sitting down near your attorneys is perfectly appropriate. Being sad, and even crying is ok too if and when appropriate. However, under no circumstances should you ever laugh or roll your eyes or make any sarcastic gestures or remarks that would suggest that you are overconfident in your case, because this type of behavior will turn a big case into a much smaller case and a small case into a no-case. Few things turn off jurors more than overconfidence or sarcasm. This applies not only to the time when you are speaking in front of the jury but also to every other moment during the court proceedings. Remember - there are 12-14 people sitting and watching the trial in the state court trial. At least some of them will be looking at you at any given time, even when you are not testifying and are just waiting for the other side to present their case. You never want to be seen chuckling.
Being stoic or serious, both when you are on the stand and when you are sitting down near your attorneys is perfectly appropriate. Being sad, and even crying is ok too if and when appropriate. However, under no circumstances should you ever laugh or roll your eyes or make any sarcastic gestures or remarks that would suggest that you are overconfident in your case, because this type of behavior will turn a big case into a much smaller case and a small case into a no-case. Few things turn off jurors more than overconfidence or sarcasm. This applies not only to the time when you are speaking in front of the jury but also to every other moment during the court proceedings. Remember - there are 12-14 people sitting and watching the trial in the state court trial. At least some of them will be looking at you at any given time, even when you are not testifying and are just waiting for the other side to present their case. You never want to be seen chuckling.