Why dont you just show him how its done , so he knows exactly what is what before you find yourself up on a roof with a liability, you cant expect him to know how to erect a chimney if he has never done one before, he probably only ever done that training centre saddle with the other trainees,
So I suggest you do him a favour , yourself a favour , all scaffolders and the industry in general a Big Favour and teach the c@nt how to do one, rather than stick a picture under his snout and coming on here .
Sorry Mr B , But guidance not Ridicule , is the Answer.