'Who's your fat friend?' was really good.

It is well known, in all probability, that George IV. contemplated with
as much disgust and horror the increasing rotundity of his 'presence' as
ever a maiden lady of a certain age did her first grey hair. Soon after
the bell affair, the royal beau met his former friend in St. James's
Street, and resolved to cut him. This was attacking Brummell with his
own pet weapon, but not with success. Each antagonist was leaning on the
arm of a friend. 'Jack Lee,' who was thus supporting the Beau, was
intimate with the Prince, who, to make the cut the more marked, stopped
and talked to him without taking the slightest notice of Brummell. After
a time both parties moved on, and then came the moment of triumph and
revenge. It was sublime! Turning round half way, so that his words could
not fail to be heard by the retreating Regent, the Beau asked of his
companion in his usual drawl, 'Well, Jack, who's your fat friend?' The
coolness, presumption, and impertinence of the question perhaps made it
the best thing the Beau ever said, and from that time the Prince took
care not to risk another encounter with him.[11]

[11: Another version, given by Captain Jesse, represents this to have
taken place at a ball given at the Argyle Rooms in July, 1813, by Lord
Alvanley, Sir Henry Miklmav, Mr. Pierrepoint, and Mr. Brummell.]

Brummell was scotched rather than killed by the Prince's indifference.
He at once resolved to patronise his brother, the Duke of York, and
found in him a truer friend. The duchess, who had a particular fondness
for dogs, of which she is said to have kept no fewer, at one time, than
a hundred, added the puppy Brummell to the list, and treated him with a
kindness in which little condescension was mixed. But neither impudence
nor the blood-royal can keep a man out of debt, especially when he