In late June 1801, the Bishop of Lincoln wrote to Mr. Pitt asking him to visit Buckden Palace. Pitt's niece Miss Eliot, the only daughter of Pitt's late sister Lady Harriot Eliot, was at Buckden, and the Bishop hoped that Miss Eliot's presence there would serve as an inducement. It looks like Pitt wasn’t keen on coming to Buckden - or to the Commencement ceremony at Cambridge. Pitt had resigned as First Lord of the Treasury in the previous February. Clearly, Pitt's unpromising response to the Bishop's invitation did not go down well, as Lincoln wrote on July 4th:
“We have been all greatly mortified & surprised at not hearing from you, & I really am most seriously concerned at the little hope you express in the Letter I have this instant received from you of being able to attend the Commencement. Indeed, my Dear Sir, you are not aware of the importance of your presence at Cambridge at this moment. I hear from all quarters that an opposition to you is intended, & you will recollect that it is more than five years [?] since you were there. If possible, pray set out to-morrow or very early on Monday morning We shall go to Cambridge to-night or to-morrow morning, & the Commencement is over. Lord & Lady Bathurst are to dine with us on Tuesday at five o’clock…Miss Eliot takes this Letter to Town - we have been more delighted with her than ever. Mrs. Pretyman & myself have been dreadfully disappointed that you did not meet Miss Eliot at Buckden & I really believe that she [Miss Eliot] too has felt very much. Adieu my Dearest Sir. Mrs. Pretyman desires her best Compts. - she is always sensible of your kindness.” 
Of course, the Bishop of Lincoln wasn't being pushy or passive aggressive whatsoever. ;)
Pitt did manage a visit to Buckden Palace in December 1801, and more information on that visit can be read here.
1. George Lincoln at Buckden Palace to William Pitt, July 4, 1801. British Library Add Ms 89036/1/8, f. 40.