Jason Gardiner, the choreographer and television fashion expert, was walking along Stockwell Road, south London, at about 7.30pm on Sunday when he was accosted by two youths wearing hooded tops.
They held a knife to his throat, threatened to kill him and ordered him to hand over his mobile phone before making off, he has told police.
The 40-year-old Australian, who is said to have been deeply shaken by the experience, posted a message on Twitter, where he has more than 83,000 followers, later in the evening explaining what had happened to him.
“Tonight I was mugged by two hooded black youths in Stockwell who held a knife to my throat and threatened to kill me, all for an iPhone,” he wrote.
A few moments later he added: “Apart from being shaken I’m fine! I’m saddened more than anything and disgusted with where our society is heading.”
But his description was criticised by some. Lee McVeigh, 25, from Brighton, wrote: “Not really necessary to drop in the fact they were black . . . ”
Mr Gardiner, who offers daily fashion advice on the ITV programme This Morning, was quickly drawn into the debate, tweeting: “Yes it is. It’s not racist, it’s a vital fact in case anyone can help and report them to the police.”
The explanation was ridiculed by some. Mr McVeigh wrote: “Everyone look out for two hooded black youths in Stockwell with an iPhone–not much of a description.”
But a string of others rushed to his defence. One wrote: “How can the race card be used when someone was mugged? Seriously!”
Vicky Entwistle, the Coronation Street actress, posted a message offering her sympathy: “Hope you are OK Darling, sending you a big hug,” she wrote.
A Scotland Yard spokesman confirmed that police are investigating a robbery on a 40-year-old man on Stockwell Road on Sunday evening. No one has been arrested.