I like the two answers given already, especially 'antithesis', but would also offer up:

Nadir  http://www.merriam-webster.com/dictionary/nadir

"The worst or lowest point of something"

In some (not all) cases I think it's a better fit.

eg: "she looked [like] the nadir of elegance and good taste"

I like the two answers given already, especially 'antithesis', but would also offer up:

Nadir 

http://www.merriam-webster.com/dictionary/nadir

"The worst or lowest point of something"

In some (not all) cases I think it's a better fit.

eg: "she looked [like] the nadir of elegance and good taste"