Arguments are most nerve-wracking when the characters imply what they feel instead of coming right out and saying it. In fact, the more intense the feelings, the more likely people are to say the opposite of what they really mean. If you want to keep up a high level of tension, keep the dialogue evasive, filled with suppressed information and unstated emotions. Once people really are candid, once the unstated becomes stated, the tension is released, and the effect is cathartic. If you’re trying to build pressure, don’t take the lid off the pot.