Ah, that is good news that they are back to original relationship! In trying to do that, it can be best to just wait for the moodlets to be over, and/or work on that by Calming Down In The Mirror for Anger, Hide Under The Covers for Embarrassment, or use the menu interactions on the other Sim to do a Smooth Recovery, etc, that are meant for the alleviating the emotions. They're easy to spot as they have the same color as the emotion on their little icons. It's also hard to work on getting the relationship back in the green if they are Uncomfortable or Tense, so one can work on that. When they're back to a more positive moodlet, the interactions so much more smoothly and increase the bars more quickly. If you want them to do something that will last a while, you can select Cloud- or Stargazing if you have Outdoor Retreat. It builds Friendship slowly, but will last around a Sim half hour.
If you need to get Angry, the Lion Animal Hat will do it. These hats came with TS4 Digital Deluxe Upgrade. It is offered free from time to time if you don't have this content. You just click Plan Outfit on a dresser or mirror and go into CAS. If a household Sim is Hotheaded and/or gets randomly angry for other reasons, you can have them cook Flaming Hot Spaghetti, and have the other Sim eat it. If all else fails, just pick a random Sim walking by the house and do some Mean interactions until you Declare Enemy, and that should do it as well. Then you won't mess up your important relationships.
