Vespasian was square-bodied, with strong, well-proportioned limbs, but always wore a strained expression on his face; so that once, when he asked a well-known wit: 'Why not make a joke about me?' the answer came: 'I will, when you have finished relieving yourself.'
That joke would be mildly funny if were to take place today, but it's an absolute riot given that it was told a couple of millennia ago about one of the Roman emperors, to that emperor's face, and recorded for all of posterity by one of the world's eminent historians, Suetonious.
And it says something positive about Vespasian's character and sense of humor that he did not have that "well-known wit" killed immediately. (Perhaps he did, but there's no indication of that here, and I'm going with the thought that Vespasian followed it up with, "Ya got me there!")
OK, I'm finished. You may tell your joke now.