I have found that to do cryptic crossword clues, always assume it's an anagram.
As for the joke I posted, I grew up reading books on synonyms, which explained the subtle differences between the meanings of similar words, and my brain, when reading the bus joke, was in that mode, wondering whether there was such a difference between exhausted and tired, and also remembering something my friend told me, that being first and at the front in a race is more tiring than being second.
