Joscelin story is that he escaped from Kharput all the way to the Euphrates. His shoes wore out along the way, then he had to inflate two leather bags to float across the river because he couldn’t swim. He then fell asleep under a tree and covered himself with branches and thorns. He wasn’t alone though, and one of the servants who escaped with him found a peasant and begged him for some food, but the peasant recognized Joscelin right away. Then Joscelin travelled with the peasant’s family and carried the peasant’s daughter on his lap, although the girl cried so much that he was afraid he would be discovered. This always reminds me of the final episode of MASH…fortunately Joscelin did not abandon or suffocate the child, because he “perceived that this would upset the peasant”! What an understatement! Eventually he arrived safely back in his own territory.

The story is from Fulcher of Chartres’ chronicle, but Fulcher doesn’t say how the peasant recognized Joscelin.

Another example is King Richard I of England, who disguised himself on the way back home after the Third Crusade because he ended up in the territory of the Holy Roman Emperor. The emperor’s relative Conrad of Montferrat, the king of Jerusalem, had been assassinated during the crusade, and Richard was suspected of hiring the assassins. He had also offended another relative of the emperor, Duke Leopold of Austria. So he dressed up as a pilgrim, and at one point he was apparently dressed as a cook - when the Emperor’s men found him he was holding a chicken. He was discovered because he either spent a suspicious amount of money in the little town where he was hiding, or because he was wearing a ring that was obviously too valuable for the type of person he was pretending to be.

A third example is William Longchamp, who governed England while Richard was away on crusade. He was eventually deposed by Richard’s brother John. William disguised himself and tried to escape to the continent, but when he tried to arrange transport, he only spoke French and couldn't communicate with the English; then he also tried to disguise himself as a woman, but a fisherman apparently found him pretty attractive and tried to get in his pants.

There may be some fantastical elements here - clearly, if they are not entirely tall tales, they’ve probably been exaggerated by whoever was telling the story before it was written down. But there is a common theme. In Monty Python and the Holy Grail, the peasants know Arthur is a king because “he hasn’t got shit all over him” - a joke, of course, but in real life, it was the same idea: a nobleman in disguise must have simply looked and acted strange in the eyes of the peasants.

Aside from the source you mentioned, my source for Richard and William Longchamp is John Gillingham, Richard I (Yale University Press, 1999).