Malandrón is a slang term that loosely translates to "thug" or "bad boy". It's derived from malandro, which means a delinquent or gangster.
In the song, the singer describes himself as "un poco malandrón" (a little bit of a bad boy). He uses it to build a persona of a tough, street-smart guy who is also charming and protective, creating a classic "bad boy with a heart of gold" image. It's a great example of modern slang used to convey a specific identity in music.
This song is all about a classic 'bad boy' who has fallen for a 'good girl,' and he knows her friends don't approve. He lays it all out from the start: "Tus amigas dicen que no valgo la pena" (Your friends say I'm not worth it). He presents himself as a dangerous choice, calling himself a "castigo" (punishment) for the beautiful "princesa" (princess). He's not rich and admits he's "un poco malandrón" (a bit of a thug), but he promises to protect her.
He argues that their connection is more than just physical, telling her friends they're "Tontitas, si supieran que no son deslices" (Silly girls, if only they knew these aren't just flings). The whole thing is summed up perfectly with one of the best lines: "Tú eres Barbie, yo, tu Ken de acción" (You are Barbie, I am your Action Ken). He's not the clean-cut, perfect boyfriend; he's the rough-around-the-edges version, and he thinks that's exactly what she wants.