When something is is totally disgusting, gross or just plain sucks! Especially smells (oh god, that was rankin!!), but it can describe anything, from taste, to how you feel, to the clothes someone dorky kid wears(those shoes are rankin, you nerd)
Even if something's just totally uncool-"yeah, your hairstyle is like,kinda rankin dont you think??"
If you're having a bad day -" Aww man, this day has been Rankin"
Or if you've eating something that was really gross-"YUK!! that was RANKIN!!"
"This public toilet is rankin!!"