1. En pelotas

This literally means “in balls” (hence the photo) per the modern definition of “pelota”, but that’s not what it refers to at all (it’s not using the modern definition of “pelota”). Contrary to what many people think, “pelota” here doesn’t mean “ball” at all.

Its origin actually stretches back to at least the 14th century, possibly earlier. It started with the phrase “en pellote”, which meant “naked”; the word “pellote” is an antiquated word that means “skin”.

The problem is, that I alluded to above, is that in modern times it has come to be associated with “balls”, that is a man’s testicles. This results in people incorrectly assuming it only applies to men, or only originally applied to men and has since been expanded to refer to women as well. This is completely incorrect, “pelota” refers to an outdated Spanish word for “skin”, and the phrase isn’t the least bit sexist.

Source (and if you’d like to read more, be warned that it’s in Spanish and contains a photo of naked people, though): https://es.wikipedia.org/wiki/En_pelota

Some contextual, real-life examples from Reverso Contexto: