It's a slang term and is not typically used in polite conversation.
Here's why:
* Mocos: This is the Spanish word for "boogers" or "snot."
* Locos: This means "crazy" or "insane."
Putting these together, "los mocos locos" is a humorous and somewhat vulgar way to describe someone who has a lot of snot or who is acting in a silly or childish way.
It's important to note that this phrase is rarely used in everyday conversation and is usually considered offensive or childish.
If you hear someone use this phrase, it's likely that they are joking around or being sarcastic.