Placoso is a popular slang term in Regional Mexican music that describes a person with a confident, showy, and often intimidating style or attitude, like a 'boss' or someone with a lot of swagger.
In the song, the singer says, "Siempre placoso" (Always placoso), to describe his cool and untouchable demeanor after the breakup. Learning this word is a key to understanding the confident vibe of the corridos tumbados genre.
This song is one of the most direct breakup anthems you'll ever hear. The singer has just found out his girlfriend was cheating on him, and he is not holding back. He opens by calling her "Falsa" [Fake] and telling her "vete a la chingada" [go to hell]. He feels like a fool for believing she loved him, singing "Y de pendejo me veías la cara" [And you were making a fool of me].
Instead of being sad, he gets even. His new life involves partying with his friends ("camaradas"), spending lots of money, and meeting new women. He makes it clear he's done with serious relationships, saying "No me enamoro, estoy mejor solo" [I don't fall in love, I'm better off alone]. He even taunts his ex by saying her own friends are now dancing for him. It's a song full of anger, pride, and the decision to enjoy the single life after being betrayed.