The Amateur Historian is sure the joke made more sense when drunk.
However, one of the most amusing of his university experiences had to be when he was invited to the country estate of his friend, Henry Bankes, along with William Wilberforce and a number of others. Pitt readily accepted this invitation, as he was a younger son without a country estate and London (this was at the beginning of the industrial revolution, and also at a point where London was one of the msot populated cities on the planet) was said to be deadly in the summer. While they were there, Pitt and his friends engaged in some grouse shooting.
No record remains of what they shot, except that the short-sighted Wilberforce took aim at Pitt and nearly shot him in the head by mistake.
Grouse shooting later came back to haunt Pitt the Younger; in 1797, his bill to introduce some regulation and social security for child laborers failed when the MPs decided they'd rather debate grouse-shooting insted.
Wilberforce got the worst end. For the rest of his life, his friends teased him for having taken "a shot a greatness" and missed.