Ser más malo que la sarna
 

How do we say ser más malo que la sarna en English?

"To be worse than scabies" is the only thing I found. I'm not familiar with the Spanish idiom (what it might mean other than the literal meaning). I've not heard the literal English translation, either, so we need an idea of what the expression means.

Sarna is mange in English. I assume that is a person compared to mange would be a very annoying type. If that is the case, calling the person a pest would be an acceptable translation.

Sarna is mange, when used in conjunction with an animal, and scabies when a human is so afflicted.

There are many set expressions with the comparison "ser más malo que...", which use a colloquial construction, because "good Spanish" would prefer "ser peor que...". You will certainly find them with "peor", but the most frequently heard sentences are usually with "más malo".

They generally mean that someone is such a bad person, that if you meet them, it's worse for you than getting a disease. Or that you got in such a bad situation, that you'd be better off if you got the disease. :)

You may find other similar expressions in Mexico:
- Este fulano es más malo que la carne de puerco/marrano.
This guy is even worse than pork meat. (Pork meat has a bad reputation, I'm not really sure why.)
- Ese chiste es más malo que un dolor de muelas.
That joke is worse than getting a toothache.
- Eres más malo que el aguacate después de un coraje.
You're meaner than eating avocado after getting mad. (For some reason, we believe you must not eat egg or avocado if during the previous minutes you have been angry.)

And I found online also: "ser más malo que la tiña", "ser más malo que la peste", "ser más malo que la quina" (this one seems to be a supplement similar to Scott's Emulsion). :D