1. (Interj.) A filler word, used to start sentances in place of words like "hey," or to add emphasis.
2. (Pron.)A way to address a group of people.
Note the distinct difference from Dude Guys I Don't Know (DGIDK)
Dude guys, where's my phone?
Dude guys, I'm ripshit pissed!
Hey dude guys, where you at?