Woohoo is the ultimate expression of love in The Sims 4, that is, unless you're going for the Serial Romantic Aspiration. The Woohoo interaction, along with Try for Baby, is a fun relationship booster that appears once a Sim couple has enough Romantic Relationship built up (the bottom, pink bar). Woohoo will make Sims happy in that it gives a 4h moodlet and raises Fun and Social needs, though slightly decreases hygiene. In this Guide, we'll reveal factors that affect likelihood of a successful Woohoo and where Sims can do it.

Woohoo is available to all Sims Young Adult and up, and may be performed between any combinations of gender. Sims can also Woohoo with Ghosts, and there is actually an achievement for that, along with a couple of others related to Woohoo that are listed below. Teen Sims do not get Woohoo, but are able to Mess Around. The mechanics for that are similar to Woohoo. Sims need to have a relationship standing of around 40-50% in Romance to get it to appear. If two Sims are Married, Engaged, or Girlfriend/Boyfriend they should always have the option. The higher your relationship with them, the more likely they are to accept. There are other factors as well:

Boosting Woohoo Success, and Factors that Lower it
Sims who have a high Charisma Skill are more likely to have their Woohoo interaction accepted by another Sim. Additionally, those with the Alluring Trait are 20% more likely to find success and have a +2 effective Charisma Skill Level. You get this trait by choosing a Love Aspiration when creating the Sim. Moods also affect it. Flirty has the biggest impact, while Playful and Happy is also helpful. If a Sim is Sad, Angry, Embarrassed, Stressed, or Bored, they are less likely to engage in Woohoo with your Sim. See the Romance Guide for more detailed info. When they're in a bad mood, improve it somehow, by filling their needs or cheering them up with a social, then try to Woohoo! You can learn more on improving Relationship standing with a Sim in the Relationships and Making Friends in The Sims 4 Guide.