There isn't one person or thing I would make disappear. I am highly satisfied with my life, so removing a thing or person could drastically change who I am today.
For example, my HS Chem teacher was an *** to me... she was always on my case and summoned my mom to school to conference with her. I disliked that Chem teacher so much that my grades were affected, and ultimately I decided against a career in Medicine and opted for Engineering. This turn of events was what eventually lead me to meet my DW. Another example is Gen. Manuel Noriega, he had a terrible effect on my life, my family's business and lives, most of my friends, etc., but he and his corrupt and repressive regime is what forced my decision to move stateside.
I could go on and on and on about why something or somebody may have a negative effect, but in the end it has all worked out for the best and I would not change a thing.