2 things people are in total denial of

Being a pessimist
Being a micromanager

Anyone who is considered one of the above by those around them will, without a doubt, be in total denial that they are one.

Ever seen a manager admit their a micromanager - generally micromanager bosses are the ones that preach how much they hate micromanagers and often verbalize that they "difinately" are not a micromanager. It usually sounds something like this, "I don't want to micromanage you, but did you..."

Pessimist - no one will ever admit to being a pessimist. Calling them a pessimist generally means you're now looking at an angry pessimist.