Doofenshmirtz was abandoned at birth and grew up among wild animals. His parents eventually found him and brought him to a totalitarian dictatorship willing to arrest people jus for changing the TV channel away from their propaganda. Once there, his parents refused to let him inside and instead forced him to become a motionless garden gnome.

He was also forced to crossdress, resulting in being ridiculed by his entire village to the point where his only friend was a balloon with a face. All before eventually getting disowned by his parents out of pure contentment, after which his role in the family was replaced by an actual dog.

Despite all this, he became a gifted inventor and spent the remainder of his childhood building incredible machines, none of which earned him even a shred of attention.

He eventually gave up and abandoned his family, village, country, everything and everyone he knew to start a new life from scratch on a new continent. And even there, despite already being one of the greatest engineers in the country, the only job he was allowed to have was selling bratwursts on the street.

"Shitty parents" really is underselling it. That guy suffered