Desahogarme is a fantastic verb that means "to vent" or "to unburden myself". It's a very visual word, as it literally translates to "to un-drown myself" from the verb ahogar (to drown).
In the song, the narrator sings about going out with friends pa' desahogarme (to vent). He's trying to escape the feeling of drowning in his sorrow after a painful breakup. It's a powerful and relatable word for expressing emotional release.
This song is one of the most direct breakup anthems you'll ever hear. The title, "Vete a la fregada," is a very strong way of telling someone to get lost or go to hell. The singer has just discovered their partner with someone else and realizes the whole relationship was a lie. They sing, "Así como un juego, muy bien me jugaste" [Like a game, you played me very well], after seeing them with a new person.
The lyrics perfectly capture that messy mix of sadness and anger after a betrayal. The singer's feelings flip from love to pure hate: "Antes yo te amaba y ahora te odio" [I used to love you and now I hate you]. They try to wish their ex well with the new person, but immediately take it back with a classic line: "Ojalá que te bese mucho mejor... Miento, ojalá te haga sufrir" [I hope he kisses you much better... I'm lying, I hope he makes you suffer]. To cope, they go out drinking with friends, but it doesn't work. It just makes them want to call their ex and tell them how much it hurts.