creepy, iffy, fairly unsafe, an air of uncertainty, not kosher, and just generally something or someone that you don't want to be associated with (or really do want to be associated with, depending on who you are...)
sketchy sketchy restuarant that is defined by it's sketchiness. has a certain culture about it: "great" coffee, hasbrowns scattered and smothered, and the classic waffle. frequently visited in the middle of the night by drunk and/or high college students.
"What is there to do at 2 am around here? Let's go to Waffle House!"