Why would he need a choice? Would you ask him if it was ok to call him Sooty? Surely that gives the impression that calling him Sooty is somehow wrong or racist.
I know you don't mean it to be racist. But that is the bit where I wanted @motorbiking's opinion. My gut feeling is that it might make a difference, legally. I'm not talking about your situation, specifically. I'm interested in the law generally and am asking whether that is the sort of thing which might be a factor.
