By definition hypocrisy is:
the practice of claiming to have moral standards or beliefs to which one's own behavior does not conform
To illustrate an analogy, hypocrisy means that you claim to be 100, when you're 50. (higher number means better)
Search for hypocrisy's antonyms and the most mentioned word I could find, was sincerity, which is:
the quality of being free from pretense, deceit, or hypocrisy.
Again, using numbers illustration, it means that if you are 50, you show 50.
I'm searching for a word to describe that you're 50, but you show 25. I can think of modesty. However, just like hypocrisy which is a negative trait (with negative connotation), I'm searching for a negative word. Modesty is good. I would enjoy being called a modest person. Maybe modest can be compared with self-confident, which is to show yourself bigger, but in a positive and welcomed way.
What word can describe showing less, but in an unpleasant way best?