David Kennedy Culzean Castle

I have looked into a few of Boswell's journals concerning this. 

Boswell and the Kennedy family were probably well acquainted even before Boswell himself became an advocate in 1766, and thus became a professional colleague of David Kennedy in Edinburgh. As early as 1764 Boswell, then visiting the court of Gotha, in a journal entry likened David's brother, the 9th Earl, to the chamberlain of that court. Boswell mentions Kennedy a few times in 1767 when the two were at the same gatherings and dinners.

Kennedy became a Member of Parliament in 1768, and in 1769 Boswell stopped keeping a complete journal for a few years, so there does not appear to be any references to the relationship between the two in these years. 

On March 20, 1772, Boswell visited David Kennedy in London and "had a laugh with him". On April 5, 1773 Boswell paid another visit to Kennedy and noted in his journal that "[I] found him the same joker as formerly and nothing more. It struck me a little to think that the gentlemen of Ayrshire should be represented in Parliament by a good, honest, merry fellow indeed, but one so totally incapable of the business of legislation, and so devoid of the talent that distinguish a man in public life." Boswell then described how "[I] went into the humorous rattling style and plagued him with a new-invented dialogue between his brother, Lord Cassillis, and him ...". From the journal entry and Boswell's tone it would appear that Kennedy clearly was used to Boswell's jests, and apparently was not averse to them. Afterwards Kennedy took Boswell to a session in the House of Commons.

Boswell, "put[ting] allegiance to feudal principle before candidate" (Boswell for the Defence, p. 211) supported Kennedy in his unsuccessful re-election bid against Sir Adam Fergusson in 1774.

I have not looked through the later journals yet.

As I see it, James Boswell and David Kennedy were on cordial terms, both enjoying a good laugh and merry company. David does not appear to have been particularly vain, and may to some extent even have agreed with Boswell's characterisation of him. Apparently he sat in the House of Commons for six years, and only spoke once, which could suggest that he was himself aware of his, perhaps, lack of talents as a public speaker. This is speculation, of course, but based on Boswell's journal entries it seems a reasonable interpretation of Kennedy's personality and his relationship with Boswell.

I have yet to trace the verse you quote, but I'll let you know if I find anything.

Best wishes,

Thomas

Had a look in Boswell's later journals, and found this in "Boswell: The Applause of the Jury, 1782-1785":

Thursday 7 November [1782]:

Walked to the village of Auchinleck and rouped the farm of Stonebriggs; dined with Mr. Dun, and came home pleased with self and everybody. Found Mr. and Mrs. Hamiltons (Sundrum). Was glad to see them, and spent the night in agreeable mirth, towards which an extempore verse of a song upon the Earl of Cassillis and Miss Coopers greatly contributed.

The text for this verse is printed in a footnote to the entry by the Yale editors, who also note that "The Miss Coopers may have been daughters of Sir Grey Cooper. If so, their mother was a Kennedy."

It also seems clear that Boswell and Cassillis were at least on visiting terms and occassionally supped together in the first years after Boswell inherited Auchinleck House in 1782.

-Thomas