Groserías translates to "swear words," "profanity," or "rudeness." It's a fantastic word to know for expressing when something is vulgar or impolite.
In this song, Rels B uses it in a very self-aware way. After a few explicit lines, he sings, "Perdona groserías" (Forgive my swear words), directly apologizing to his lover—and the listener—for his language. This clever, meta-lyric is an intriguing hook that makes you want to hear what he has to apologize for.
Rels B gets straight to the point in "Cómo Dormiste?". The whole song is a fantasy about waking up next to someone and immediately wanting them. He skips the small talk, imagining a morning that starts with sex instead of conversation: "Prender sin decir 'Buenos días'" [Turn on without saying 'Good morning']. The title comes from the question he wants to ask right after: "'¿Cómo dormiste, bebé?', Si me soñaste" ['How did you sleep, baby?', Did you dream of me?]. He's not just asking if she had a good night's sleep; he wants to know if he was in her dreams and if she woke up wanting him even more.
From there, the song gets very explicit and confident. Rels B mixes compliments with some pretty blunt descriptions of sex. He calls her an expert, comparing her to something from "Dexter's laboratory", and uses modern references like the brand Supreme to describe a red mark on her skin. He lays out exactly what he thinks she likes, from aggressive dembow music to how he treats her in bed. The track is built around this contrast between the sweet, almost caring question of "How did you sleep?" and the incredibly direct, crude language he uses to describe their physical connection.