"Barista" is not a Spanish word, and many barmen in Spain might feel their virility was being doubted if you used the word to them, since most Spanish words ending in "a" are feminine. ("Camarero" is the Spanish word for barman.) "Barista" is, however, the Italian for barman or barmaid. Clearly, both that word and "barrister" are derived from the word "bar" (or more accurately from the Latin "barra") but in one case it's a bar for dispensing drinks, and the other justice.