Stephen Davies, who says he was sexually harassed by a female colleague, undid his trousers in front of dozens of people after being challenged about the size of his penis.
The incident was one of several instances of bad behaviour, sexual excesses and drunkenness alleged to have taken place among agency staff in the run-up to its launch in April 1993.
The tribunal in Birmingham has been told that a 35-year-old CSA official - who can be named only as Mrs A - accused Mr Davies of sexual harassment because he refused to sleep with her. He is accusing the CSA of sexual discrimination because its poor equal opportunities policy failed to stop her sexually harassing him.
Asked by Alastair Smail, counsel for the CSA, to describe the trouser- dropping incident, Mr Davies, former project operations manager, said: 'At the launch party of the CSA centre in Dudley (West Midlands), in front of 50 to 75 people who were standing on a balcony, as I left the building with other people, someone - I don't know who, presumably a friend of (Mrs A's) - shouted from the balcony: 'Steve, is it true you've got the biggest prick in the CSA?'
'I turned round, undid my trousers, and turned my back to the people, but I didn't reveal anything to the best of my knowledge.'
Mr Smail said Mr Davies's claims of sexual harassment were the acts of a desperate man. He was cleared of sexual harassment against Mrs A but was sacked in March after being accused of managerial harassment of two other women.
'The truth is that this is your come-uppance time and you're having difficulty dealing with it,' Mr Smail said.
On Tuesday, Mr Davies admitted having had other affairs and accused Mrs A of having one. Yesterday, in a statement read out by Mr Smail, Mrs A's husband, also a CSA employee, said he had told Mr Davies that he, too, was having an affair with another CSA official - Mrs C, who also cannot be named.
But Mr Smail said the claim of an affair was a device to protect Mrs C, who had been 'pestered' by Mr Davies at two CSA social events. It was also normal for other CSA staff to take turns keeping an eye on Mrs C because of Mr Davies's unwelcome attentions, he said.
Mr A said that a drunken Mr Davies had once laid a bet that he would sleep with Mrs C despite her rejection of his advances.
Mr Davies denied the claim and indicated that Mr A's advances towards Mrs C were real and were made in Newcastle during a training visit. Mr Davies had offered to walk Mrs C and another CSA employee to their hotels but was asked not to by Mr A. '(Mr A) approached me in the toilet and said he would take the girls home because he was seeing (Mrs C),' he said.
'The following day, he informed me that (Mrs C) was having problems with her husband and was considering leaving him. To (Mr A) the relationship was serious, but (Mrs C) was keeping him at arm's length. She had rejected his first clumsy sexual advances but he thought it would be all right if he could spend more time with her.'
Another woman, known as Miss E, made a statement that immediately after the trouser-droppping incident, she had gone home with Mr Davies, a married father of two, and indulged in 'rather more than a goodnight kiss', according to Mr Smail. Mr Davies admitted the incident but said it was no more than a goodnight kiss.
Miss E also alleged that at another party, Mr Davies said he was being pestered by a woman who he believed fancied him. 'You asked her to kiss you in front of this woman so she would stop pestering you?' Mr Smail said. '(Miss E) refused and your attitude to her changed completely. You told her that her career was finished.'
Mr Davis denied that allegation and another from Mr A that he tried to get rid of another staff member, Miss B, because she would not sleep with him.
Towards the end of his evidence, the hearing was brought to a halt when Mr Davies accused Mrs A of smirking at him. 'I find it very disconcerting that she has been smirking at me all through this tribunal,' he said. 'And I know what a smirk is.' The tribunal chairman, asked Mrs A to compose herself.
The hearing continues today.
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