People who have not matured tend to have little emotional control, and they can exhibit this lack of ability in many ways. As children, they may have a temper tantrum when they do not get what they want. Most of them grow out of that phase by the time they are teenagers, but adults who have never been expected to control their temper learn different methods. They tend to claim they are passionate about something, but it may eventually be questioned by their partner whether it is passion or temper that makes them behave badly.
Failure to get their way immediately might result in the immature partner choosing the passive-aggressive method of dealing with the situation. They will become silent and refuse to speak about what is bothering them, but they will then behave aggressively when their partner is unable to discover the issue. This method has been a tried and true answer for many who refuse to grow up, but it can eventually become a sticking point in the relationship.
Public meltdowns by adults have been frowned upon by society as a whole, but they still occur. Those who want something are often unwilling to stop until they get it, and they may become verbally abusive to their partner before other people. They generally stop short of physical violence, but that does not mean it will not happen later in private. Their screaming and shouting can take many different paths. They might cite their need to have the object in question in a passionate manner, or they could lose their temper and revert to the behavior patterns of small children.
Living with someone who refuses to mature into an adult can be difficult, and it can take many forms. Some immature people act as if they are simply passionate in their needs, but they are really displaying their temper when they do not get what they want. It might take time to be able to tell the difference, but the person they are in a relationship with might soon figure out they will never grow up.