Something most jank and hideous which stings the eyes, someone who everyone looks at in an animalistic way as they are not human they are too ugly to be human. although they have a fitcousin.
you see that girlover there buddy?
Oh yeah, thats milly she is most heinous.
Although heinous traditionally means evil, it is used by many teenage girls to describe someone that is so horribly ugly or disgusting that it is almost evil in itself for that person to look that way.
The word is not just used to describe extremely unattractive people, but it can also be applied to objects--especially clothing apparel.
Mary: I think she is pretty.
Jess: Are you kidding? I think she's heinous.
Christina: What do you think of this sweater?
Jess: That is the most heinous thing I've ever seen.
Marissa: Do you want to go to the mall tomorrow with me and Johnny?
Jess: Ew!!!! Why do you hang out with him? He is SO heinous!!