Cool bums who hang out on mill ave in tempe, arizona. Often these people are artists, who will make you things or preform for you if you give them attention.
Person A: Dude, Happy Cabbie made me a hat that looks like a fish out of balloons!
Person B: Dude, he's my favorite mill rat.
An utterly despicable waste of space that inhabits Mill Ave., in Tempe, AZ. They pass themselves off as artists when in all reality they are no-talent-ass-clown-college-drop-outs that survive off of the donations of others nearly as retarded as they are.
The Mill Rat is sleeping in vomit.
The Mill Rat is consuming vomit.
The Mill Rat is covered in my vomit.