Although that's hell of a temptation, unfortunately it could have wide ranging effects. The forum is public and other visitors could get thwacked with such a post. Collateral damage, I think they call it. Also, as a mod, I'd be placing DW in a very bad light if I did such a thing. :( The devil's whispering in my left ear as we speak! "Do it...you know you want to..."
Trouble is for most members, once you've gone past the 30 min post period, you can't edit. It's also very rare that you'd be allowed to delete it, if it started causing embarrassment or a torrent of neg reps and downvotes. Your standing in the community could suffer somewhat - perhaps I'm being alarmist with that, but I think the best course of action would either be to ignore them or point them to a tutorial or official manual link. If it's really stupid, like "give me the codez" - then a quick polite statement should suffice.
Thing is, we want to encourage visitors not alienate them. A first time poster, for example may not realise that they've made a faux pas, and not be aware of forum etiquette. Far from being an 'ignorant, lazy, cheeky oik', they may actually be mortified to find that they'd made such an error (of judgement?) and go on to become a regular and valued contributor.