I had a similar thing (not looking at Heathrow tower I Might add) when a guy came for a check ride to Join the club. It was on a PA28 archer and he showed me pictures of his own PA28 arrow that he owns at his home town. Obviously I assumed (and there is the key word) he would be ok. Instantly I could see his checks were poor and his spatial awareness and knowledge of rules was !!!!e. I let him carry on whilst monitoring the situation and he was apauling. I took it off him on three of the four landings and suggested he do some time with the CFI. But because he oozed with confidence and owned an aircraft of same type (more complex actually) I initially took a relaxed view to the whole thing. The truth is Assume makes an ass out of you and me! those who say they are great are usually crap those who keep quiet usually fly a red arrow :-)
I once told a horse riding instructor I was an expert rider and it took off with me and bucked me off so I too have been the big mouth all be it with a sore arse! (her arse was nice by the way hence the attempt to sound like a pro)
Magpie- could you see the whites of their eyes?