The word grencha comes from the Spanish word to describe tight curly hair as in Afro-hair; I suspect that there was a racist background for the use of grencho or grencha early on but it has since evolved in El Salvador to describe an uneducated or uncultured idiot but it is also used with humor to describe an ignorant or tacky friend. So do not be alarmed if someone you are fond of calls you a grencho or grencha. I routinely call my sister grencha even though I love her dearly.
Synonyms of grencha are tacky
Used in US as well
"No seas grencha or what the hell are you wearing grencho?"