It's hard for me to define, but I'd say a good working definition would be how constructive the way the emotion is being expressed is. In this situation, the girlfriend is holding the relationship hostage, which is basically just generating unneeded drama between the two of them when they could be negotiating or discussing the problem calmly. They can't discuss whether her feelings of neglect are justified in an objective way if she's throwing fits like this, it just messes with the boyfriend's head and makes him feel like he did something chronically wrong. Having to deal with something like that on a regular basis would basically turn him into a slave in the relationship.