Mr Justice Rattee told the court yesterday that FCUK was "just a euphemism" for an for an obscene expletive.
Lawyers representing the fashion chain French Connection had asked the judge to stop an Internet consultant using the website name, fcuk.com.
They claimed the defendant was exploiting the "goodwill" generated by its successful FCUK advertising campaign around the initials it uses as its trademark.
Mr Justice Rattee asked: "How can you talk about goodwill in connection with such a tasteless and obnoxious campaign? It may be you have been hoist by your own petard in using such an extraordinary advertising slogan."
Miss Mary Vitoria, representing French Connection, replied: "Your lordship may find it offensive. I might find it offensive. But young people who buy clothes do not find it offensive, they find it amusing."
But the judge refused to give an immediate ruling in French Connection's favour. He said: "I find the case of both parties unpalatable in the extreme, having regard to the subject matter, but that is not something on which I can make a ruling."
The fashion chain had wanted an immediate injunction to bar the fcuk.com website, but the judge ordered a full trial of the issues.
The judge said that during the trial, the High Court might be able to review the registration of the trademark FCUK, and whether the registrar ought to have refused it on the grounds that it was contrary to public policy because of its obscene connotations.
The FCUK advertising campaign had been running a year before the website's domain name was registered, but French Connection did not register the FCUK trademark until some days later.
Miss Vitoria said the site had been accessed 21,000 times and was now being visited 70 times a day by people who could think it was connected with French Connection.
French Connection Ltd, which registered the trademark in April 1997, took out the action against Tony Sutton, 31, from south London. Mr Sutton, who advises on e-mail sites for companies, trades under the name First Consultant UK.
Mr Jonathan Turner, representing Mr Sutton, said the initials FCUK were widely used in Internet circles as an alternative to an offensive expletive, as a way of avoiding filters and controls on websites.
He said his client had realised the value of "fcuk" as a domain name to attract attention to his business. "It has value because it is an offensive name and was a clever way of attracting the attention of IT managers who are well-known to seek out pornographic websites on the Internet," he said.
Mr Justice Rattee asked: "It has value because it is an offensive name?"
Mr Turner replied: "It was seen as clever by the claimant, why should it not be seen as clever by the defendant?"
Earlier this year Mr Justice Rattee blocked an attempt to auction Jonathan Aitken's private letters.Reuse content