Social Bunny
The Social Bunny is a NPC who comes when Sims have a low social need. He comes in three colors which are blue, yellow, and pink. Just having the Social Bunny around raises the social need, but the lonely Sim can interact with him anyway to raise it, ranging from friendly kisses to outright fighting. The Social Bunny leaves when the bar is back up to the halfway point.
If multiple Sims are in social failure, the other bunnies will be seen when a lonely Sim is active. However, they will be transparent, and cannot be interacted with. The bunnies may interact with each other, though. Generally, ones of a different color will be friendly with each other, with blue and pink ones going romantic. However, much different sparks fly when two bunnies of the same color meet, as they'll actually fight with each other.