Chapín is a word with which many Guatemalans identify with pride. It is possible that some do not know the origin, why and the meanings that this term has had in the course of history.

The history of the origin of the word "Chapín" The chapín or chapines were a type of platform footwear of Spanish origin, which were popular and used in the 15th century in Spain. The name of these shoes arose as the onomatopoeia of the noise that the nobles made when walking through the cobbled streets: Chap, chap, chap ...

Dr. Francisco Pérez de Antón, writer and businessman, conducted studies on this issue and came to the conclusion that at one point in history the nicknames chapin and gachupín were synonymous.
Gachupín was the nickname, generalized in Mexico and Central America in the 16th and 17th centuries, that they had for the peninsular Spaniards. It was derived from the last name Cachopines and it was mockingly mentioned for being significant of someone overbearing.
In addition to the phonetic similarity of the nicknames, chapín was also used in a derogatory way for the Spaniards who resided in Santiago de Guatemala. European fashions brought "chapines" to the country during the Colony and because of the size of the platform, they caused difficulty in walking.
Gachupín was the nickname, generalized in Mexico and Central America in the 16th and 17th centuries, that they had for the peninsular Spaniards. It was derived from the last name Cachopines and it was mockingly mentioned for being significant of someone overbearing.
In addition to the phonetic similarity of the nicknames, chapín was also used in a derogatory way for the Spaniards who resided in Santiago de Guatemala. European fashions brought "chapines" to the country during the Colony and because of the size of the platform, they caused difficulty in walking.

Be that as it may, we love to be called that because we are proud of our homeland.
Original report: https://aprende.guatemala.com/cultura-guatemalteca/general/origen-palabra-chapin/