Sweary Mary is a fictional character in Viz magazine, who appeared briefly in 1994-95. Bearing more than a passing physical resemblance to The Beano‘s Minnie the Minx, her sole purpose in life was to say as many rude words as possible; and the comic's story - such as it was - revolved around her attempts to evade censorship.
The magazine was being sold in W H Smith for the first time ever during this period, and with their typical schoolboy sense of humour, the editors had placed this cartoon on the cover deliberately to cause offence. Mary's ultimate aim was to say 'cunt' on the cover - this was blocked out. Eventually, she came up with the word 'fitbin', which, the readers were told, was an incredibly rude word. As it wasn't, of course, the page was uncensored. Afterwards she still made attempts to swear on various covers and in various strips, until she finally got the chance to swear on the cover of Issue 99. Sadly, her wish was broken as she lost her voice, and the other characters taunted her as a result.
Fitbin is still occasionally heard as a swearword, although Sweary Mary, by contrast, having largely fulfilled her function, has almost completely disappeared from the pages of Viz.