Hi Anne Marie,
Güey (usually misspelled as guey, wey or we; pronounced like the English word 'way') is a word in Mexican Spanish which is commonly used to refer to any person without using his name and applies equally to males and females (though it is more often applied to males). It is used in Mexican Spanish in roughly the same way "dude" is used in modern American English. In Mexico this same word is used like an insult (can be a negative term like "fool" ), although, due to its extremely high frequency of use in a multitude of contexts, it has lost much of its offensive character, becoming a colloquialism.
According to the Academia Mexicana de la Lengua (Mexican Academy of Language), güey is a deformation of "buey" (from Lat. bos, bovis). However, a common trend in Mexican Spanish is for simple words to become very complex terms that change meaning depending on context. Güey may mean stupid, friend, enemy, asshole, deranged, courageous, and a host of terms that are inconsistent most of the time. It can be used as derogatory or superlative.
The Real Academia Española (Royal Spanish Academy) recognizes the term "güey" as a Mexican Spanish adjective to describe a fool or someone who has tripped. When used as an insult, in the uneducated lexicon, "güey" is a bull's-linguistic deviation (from Lat. bos, bovis).
Although the word is not always offensive nor an insult between friends, its usage is generally considered uneducated. Thus its usage is limited mostly to friends and trusted acquaintances or among young people. It is considered in poor taste for a teenager or a child to refer to an adult as (a) "güey," although among adults it is usually used in a common way. The word is used in any social class, being equally accepted and used in all. It also is used in television and radio in popular entertainment, but not in more formal or objective programs, like in the news.
I really Hope this helps you, Anne Marie! Have a great day!