[dekhn]

it is very, very unlikely that a fully cooked egg that sat out overnight would have enough bacterial growth (and toxin production by bacteria) to represent a threat to a normal person with a typical immune system.

If the egg had bacteria already growing in it (which is also unlikely) then it's possible that enough of the bacterial toxins could accumulate and be inside when you eat it.

There are probably a number of extremely rare scenarios which would modify the situation but this article includes a lot of words and facts only to come to the unlikely conclusion.