Oh, this is too easy.
Shitcan what you have planned for your costume already, and either go as....
1. The "drink me" bottle
-or-
2. The "eat me" cookie
Lots of innuendo and double entendre there, you know, and you can do body paint if you want to be the bottle. You just need to find someone who is good at emulating a reflective brownish glass surface with paint. (**points to self and flashes Bachelor of Fine Arts degree.***) Then all you need is to make a tag to put around your neck that says "drink me".
Trust me, it will be the most clever costume there.... unless someone else has thought of it, which they probably have.