Metal detectors only detect metal.
Lyric: "And my dick so hard it make the metal detector go off" Song: "All Me"
Maybe he doesn't know this because he flies in private planes now and doesn't have to adhere to the same TSA regulations the rest of us common travelers do, but when you go through a metal detector, it will only detect things made of metal. So even if you find yourself with a huge erection, that metal detector still won't go off, unless you have something metal near it and in that case, we have a whole other set of issues to deal with. And honestly 2 Chainz, if you have a boner that's so fierce you're setting metal detectors off, that's not something to boast about. That's a medical emergency and you should probably be seeing a doctor.