A manager at Knowsley Safari Park was sacked after allegedly using a four-letter tirade of abuse against its aristocratic owners, a tribunal heard.
The tribunal's decision will be made on Wednesday
The industrial hearing was told Sean Lawler, operations manager, "turned the air blue" when talking to Lord Edward Derby about his wife.
The couple, who own the 500-acre safari park in Prescot dismissed Mr Lawler after a list of complaints from staff.
He denied the comments and is claiming unfair dismissal at the tribunal.
The father-of-two is also accused of saying he would like to punch Lord Derby's young son.
The hearing was told four members of staff complained about Mr Lawler's "obscene and disgusting language".
The workers claimed Mr Lawler, from Wigan, who had worked at the park since 2003, also made a sexual comment about Lady Cassandra Derby.
The incidents allegedly took place between February and June 2007.
Knowsley's estate manager, Martin Harker, who chaired an internal appeal hearing by Mr Lawler against his dismissal told how the row had soured relations at the safari park.
Cross-examined by Mr Lawler's representative Mr Harker said: "The language used by Mr Lawler was grossly offensive and insulting and seemed to cast aspersions about Lord Derby's manhood.
"The Knowsley Safari Park is a family business and these comments destroyed the trust of the employees and therefore destroyed the family."