Literal translation
do good to Martin, he shits in your hand
Meaning
do good to Martin, he repays it with ill treatment
Explanation
This saying is a variant on the same theme of ingratitude, this time using the name Martin, another common first name used as an anonymous stand in, and a formula far cruder than its cousin naming Bertrand. The words to do, well, to, you, in, the, and hand are all well attested, as is the name Martin itself, while the final verb, used here bluntly in its primary, coarse sense, literally denotes the act of defecating. Unlike the more polite variant, which softens this same verb into the figurative sense of failing or disappointing, this saying fully embraces the crudeness of the image: repaying a good deed with such a gesture underscores, in the most direct and shocking way possible, the depth of contempt or ingratitude felt by the person telling the story. The register here is frankly coarse and vulgar, fit for oral use among close acquaintances or in a very relaxed setting, never in formal conversation. The moral remains the same as in the previous variant: kindness is not always rewarded, and can even be repaid with the crudest contempt.