Beer company Brewdog is embroiled in a bar brawl with the UK's advertising watchdog after being reprimanded for using "offensive" language on its website.

The ASA said that an asterisk in the independent Scottish company's description of itself as "a post-punk apocalyptic mother fu*ker of a craft brewery", was not sufficient to disguise a swearword which was "generally regarded as highly offensive and unlikely to be acceptable in marketing communications."

It ruled that the web page featuring the term should not appear again in that form. "We considered that the other language used on the page, such as 'corporate beer whores', 'rip you straight to the tits' and 'drill the bastards', was also likely to cause serious offence to some people," the ASA said.

But James Watt, co-founder of BrewDog which is in the process of raising £4m from its fans via its Equity for Punks crowdfunding scheme, responded: "We have thousands of craft beer fans who have invested in what we do and how we do it – they are the people we listen to – not the killjoy, self-important pen pushers at the ASA in their Burton suits. Those mother fuckers don't have any jurisdiction over us anyway."

The brand and its fans responded to the ASA via twitter using the hashtag #KissMyASA.

Gareth Williams@GRW_84 tweeted: "Thanks to @ASA_UK I know that @brewdog are an uncouth bunch of vagabonds with a sweary website. Turning in my share(s) #NOT" Raphaël a. gagliano@faderskepp tweeted: "I'd like to thank @ASA_UK for giving my favorite brewery @brewdog some free publicity today! Cheers!"

The fast-growing company, which trumpets its punk credentials, has made 42,000 shares available to the public at £95 each, to fund a sevenfold increase in production at its Ellon brewery near Aberdeen and to open more bars.