It's called 'sounding' and it feels amazing. When you first start it will cause discomfort for half a day after, but the feeling when doing it is hard to describe - a bit like an orgasm without having one. Sometimes I can cum just from using the rod. If you're going to start doing it, get a soft flexy rod first and a thin one!! :-)
OK I'm going to be super honest here: Could someone explain to me what's the deal with sticking a steal rod in one's own cock? What's this even called? I'd love to be educated by anyone who knows anything about this.