This was posted on alt.humor.puns by Perfect Tommy. The author is unknown.

Karl Marx was in Montmartre visiting Henri de Toulouse Lautrec. They were out riding in a carriage, and Lautrec saw some peasants working in a field and wanted to paint them. However, they were wearing dirty old dungarees, and he wanted to know if they had something more colorful to wear. Lautrec had difficulty walking because of childhood injuries, so Marx volunteered to go out to the field and ask them.

He returned, shaking his head. “I’m sorry,” he said, “the workers have nothing, Toulouse, but their jeans.”

Chris Cole added:

If ol’ Karl was out of shape and ran out and back, perhaps he, too, would be outstanding in his field, panting with the rest of them.