Rik Mayall was part of a punk-era wave of absurd/alternative comedy and he, along with Adrian Edmondson, starred or appeared in several popular British series written by Ben Elton (Young Ones, Filthy Rich and Catflap, and Blackadder) as well as the popular series Bottom and The New Statesman. He worked closely with Jennifer Saunders (of Ab Fab fame), Dawn French, Alan Rickman, Nigel Planer, and Stephen Frye. In most his roles he plays some combination of over-the-top manic and/or deeply pathetic and neurotic twit. The manic side comes across in Drop Dead Fred -- this probably helps explains his casting in the movie. I'm not sure if this style of comedy worked with a US audience, although casting him makes sense with a co-production with the UK in the early 90s when he was a mainstay of British alternative comedy.
Mayall died in June of 2014.
Trivia:
-He was almost voice cast in the Lion King but the role went to Rowan Atkinson (star of Blackadder, best know in the US as Mr. Bean)
- He was cast as Peeves the poltergeist in Harry Potter and the Philosopher's Stone, the scenes were shot but were cut. I'm willing to bet that Drop Dead Fred explains why he was cast, possibly also why the role was cut.