The ex-Partridge Family star, who became famous in the 1970s, also ridiculed the Welsh accent during his half-empty gig, The Sun has reported.
And the 54-year-old demanded silence for one of his songs during his last ever British tour.
The former pin-up even stopped playing I Think I Love You because fans were singing along.
When fans shouted, 'We love you,' he replied: "I can't listen to you and think and sing."
Caroline Tems, 46, was at the Cardiff International Arena concert.
She told The Sun: "Some women shouted and he kept saying, 'What the hell did you say? I can't understand you,'."
A spokeswoman for Cassidy said: "The weather was getting to him and he was exhausted."
― Dom Passantino (Dom Passantino), Tuesday, 11 May 2004 17:44 (twenty-two years ago)
― El Diablo Robotico (Nicole), Tuesday, 11 May 2004 17:46 (twenty-two years ago)
― Ned Raggett (Ned), Tuesday, 11 May 2004 17:47 (twenty-two years ago)
― El Diablo Robotico (Nicole), Tuesday, 11 May 2004 17:48 (twenty-two years ago)
― nickalicious (nickalicious), Tuesday, 11 May 2004 17:48 (twenty-two years ago)
― Ned Raggett (Ned), Tuesday, 11 May 2004 17:48 (twenty-two years ago)
― VengaDan Perry (Dan Perry), Tuesday, 11 May 2004 17:49 (twenty-two years ago)
― Ned Raggett (Ned), Tuesday, 11 May 2004 17:50 (twenty-two years ago)
― andy, Tuesday, 11 May 2004 17:51 (twenty-two years ago)
― Michael White (Hereward), Tuesday, 11 May 2004 17:53 (twenty-two years ago)
― Evanston Wade (EWW), Tuesday, 11 May 2004 18:12 (twenty-two years ago)
― Michael White (Hereward), Tuesday, 11 May 2004 18:14 (twenty-two years ago)
― VengaDan Perry (Dan Perry), Tuesday, 11 May 2004 18:15 (twenty-two years ago)
― Michael White (Hereward), Tuesday, 11 May 2004 18:20 (twenty-two years ago)
― David Cassidy (Anthony Miccio), Tuesday, 11 May 2004 18:23 (twenty-two years ago)
― penelope_111, Tuesday, 11 May 2004 18:24 (twenty-two years ago)
― Evanston Wade (EWW), Tuesday, 11 May 2004 18:39 (twenty-two years ago)
― Michael White (Hereward), Tuesday, 11 May 2004 18:48 (twenty-two years ago)
― NA (Nick A.), Tuesday, 11 May 2004 19:02 (twenty-two years ago)
― kyle (akmonday), Tuesday, 11 May 2004 19:31 (twenty-two years ago)
― NA (Nick A.), Tuesday, 11 May 2004 19:41 (twenty-two years ago)
― Cathy (Cathy), Wednesday, 12 May 2004 13:43 (twenty-two years ago)
― Ned Raggett (Ned), Wednesday, 12 May 2004 13:44 (twenty-two years ago)
― Cathy (Cathy), Wednesday, 12 May 2004 13:51 (twenty-two years ago)
― daffy, Wednesday, 12 May 2004 13:55 (twenty-two years ago)
― Ned Raggett (Ned), Wednesday, 12 May 2004 13:57 (twenty-two years ago)
― Cathy (Cathy), Wednesday, 12 May 2004 14:00 (twenty-two years ago)