Penis

Either you're a child, or an adult that acts like a child. Anyways, a penis is a male reproductive organ, which means it only appears in boys. The penis is used for sexual intercourse, which is the conception of another human being. The penis is both used for sexual intercourse, and urinating. Also, I recommend you don't put anything inside of it. it'll hurt like hell. And yes, that is based on experience.

John-"Dude, my penis burns for some reason."
Danny-"Haha get fucked"