Tyga Raps About Penetrating Kylie Jenner?

Tyga's got the blueprint ... brag about having sex with your juuust 18-year-old GF Kylie Jenner -- and everyone will pay attention to your new music.
Tyga just dropped a new mixtape, which includes the song, "Stimulated" -- which includes lyrics like: "They say she young ... I shoulda waited ... She a big girl, dawg ... When she stimulated."