I might not have started with what I hate about poetry - I know it recognises their issues but seems to get you off on the wrong foot. As with all stuff they don't like I'd try to get them involved through taking some kind of 'angle' or doing some poems they think of as a bit risque so they can get animated. I find this works as a starter for negatively inclined groups even if the focus is not unseen poetry. A task where poetry is turned into prose can be good at explaining the value. For your stroppy boy after the fact, I think emphasising the intellectual challenge might help, but is that something he values?