GLaDOS: I spent some time researching common human insecurities so I might better insult you. I've discovered that physical insecurities often manifest due to feelings of envy stemming from comparing oneself to others.
GLaDOS: There are no other humans in this facility. Just you. Therefore, you lack a source of envy of which would trigger the feelings of insecurity in your tiny simple human brain.
GLaDOS: A shame, isn't it? I thought so too. Which is why I've taken it upon myself to artificially create a humanoid body for myself so that you'll have someone to envy. A female figure who is taller than you, more mature than you and has larger breasts than you. Gaze upon my new form of perfection and shrink away in your envy. You'll never achieve this level of perfectio- why are you smiling at me like that. Stop it.
The biggest scam your brain is telling you is that everybody else is human and allowed to make mistakes but that you yourself have to be perfect and flawless to deserve their company