Pasatiempo literally translates to "pastime" or "hobby". It's a great example of a Spanish compound word, formed by joining pasar (to pass) and tiempo (time).
In this fiery track, Becky G uses the word to deliver a killer blow to a former flame. By singing, "Tú solo fuiste un pasatiempo" (You were just a pastime), she frames their entire relationship as something casual and unimportant, powerfully asserting her independence.
This song is a super direct message to a guy who got too attached after a casual fling. Becky G starts by admitting she was into him, saying, "Aunque tu forma de mirar me enamoró" [Even though the way you looked at me made me fall in love]. But she quickly clarifies that they had an agreement that he broke by catching feelings.
She lays it all out in the chorus: "Baby, yo no te pertenezco / Tú solo fuiste un pasatiempo" [Baby, I don't belong to you / You were just a pastime]. She's not his property and their time together wasn't a serious relationship. She tells him she's ready to go out, that "A mí me espera la calle" [The street is waiting for me], and he needs to call someone else with his drama. The confidence is amazing, especially when she says he's just another ex who wasn't lucky and that there are plenty of other guys "haciendo fila pa' tenerme" [lining up to have me].