Friend, buddy, fool, stupid, dummy.
"Way" instead of "Güey:" In Spanish, people often call someone who made a mistake or does something foolish or is a trusted buddy or a friend who will not get offended if a friend calls him "buey." But through decades, such word has evolved to "güey" because it is easier and quicker to say "güey" that "buey." "Oye güey, ¿qué onda ese?" one can say to a close friend in a sentence. Thus, the word "güey" should not be confused with the English word "way" as in: "No way."
It is both a dear person who you address to regularly, so you call it "güey" over and over, instead of using its name each time, like "dude" in english, or a person you consider not to be trustable, because it lacks of the cleverness, wisdom, or experience needed for a certain task, like an "asshole", in english. It is the right spelling in spanish for the mexican expression "wey", from which you will find similar definitions to the one I just wrote.
In case of endearment:
¡Qué onda, güey! - What's up, dude?
Sí, güey, está cabrón, güey, ya le dije, güey... - Yes, dude, it's all fucked up, dude, I've allready told her, dude...
In case of mistrust:
Nel, a ese güey no lo quiero en mi equipo - No way, I don't want that asshole in my team