I don't like when then enslavement is instant or predetermined, I really like the dynamic of corruption, barganing and surrender. So I like to imagine a totalitarian country where every citizen is assigned points and demerits for everything he does. Temporary enslavement is a very common punishment, A girl got found cheating on exams? For a few weeks, she's enslaved to her rival, the best student in the class, and has to call him master, follow him obediently, bow her head, help him study and satisfy him sexually. A girl cursed in public? She has to partake in a several day-long shibari exposition as a living statue.
There would be strict rules and regulations for such temporary slaves, you couldn't beat them up or rape them. Most would work menial jobs, like girls serving as maids or waitresses in skimpy revealing suits. You could give them a little slap on the butt or grope their breasts for a while but that's all... unless they've earned a punishment.
They would earn some points to pay for their demerits and return to society. Some people would make it easy, others would try to make it as hard as possible, always testing your obedience and submission. You forgot to call him Sir? And what was that smirk? That will extend your enslavement by another week. You spilled his drink? Better prostrate yourself and beg so he picks the least harsh from the list of punishments.
I'd like everyone to experience being enslaved at least once. Maybe like a gap year at school, though a year is way too much. You could call it "being a public servant".