Too - adverb, meaning: Very, as in "he didn't seem too bright", or Excessively, as in "too large a house for us," or to such a degree as to be regrettable, as in "This time he went too far" - another meaning is "besides, also", as in "sell the house and furniture too.
In the case of this meme, it should be "...are not TOO bright..." Using the word "to" makes no sense. Writing that phrase, "...are not to bright" demonstrates the writer wasn't TOO bright.