Buen provecho literally means "enjoy your meal" or "bon appétit." It's a common phrase said before eating.
However, in this song, it's used with a sarcastic and bitter tone. The singer, scorned by a lover who only wanted to play games, tells them, "Pa jugar te daba lo del pantalón y buen provecho." Here, it implies a dismissive "good riddance" or "enjoy what you got," suggesting the lover only got a physical encounter and nothing more meaningful, with a strong sense of irony and resentment.
Have you ever felt like you gave your whole heart to someone, only to find out they were just playing games? That's the painful feeling at the core of "BUEN PROVECHO." The singer looks back on a relationship that never became what he dreamed it would be, full of broken promises from someone who got his hopes up for no reason. He sings about falling in love deeply, only to be left hurt and deceived.
The song's central idea is regret. The singer wishes he had known his partner's true intentions. If he knew they just wanted to "play," he wouldn't have offered his true love, which he calls "el del pecho" (the one from the chest). Instead, he would have kept things purely physical, offering "lo del pantalón" (the one from the pants). The title, "Buen Provecho," which means "enjoy your meal," is used sarcastically, as if to say, "You got what you wanted from me, so I hope you enjoy it."